Treeview Shows How To Get Selected.

import tkinter as tk
import tkinter.ttk as ttk
import tkinter.font as tkfont
from tkinter import messagebox


class Treeview(ttk.Treeview):
    def __init__(self, parent, **kwargs):
        super().__init__(parent, **kwargs)
        self.parent = parent

    def fixed_map(self, option):
        style = self.parent.style

        return [elm for elm in style.map("Treeview", query_opt=option) if elm[:2] != ("!disabled", "!selected")]

    def tag_add(self, tags, item):
        self.tags_update('add', tags, item)

    def tag_remove(self, tags, item=None):
        self.tags_update('remove', tags, item)

    def tag_replace(self, old, new, item=None):
        for item in (item,) if item else self.tag_has(old):
            self.tags_update('add', new, item)
            self.tags_update('remove', old, item)

    def tags_reset(self, _=None):
        self.tag_remove(('selected', '_selected'))
        self.tag_replace('selected_odd', 'odd')
        self.tag_replace('selected_even', 'even')

    def tags_update(self, opt, tags, item):
        def get_items(node):
            items.append(node)
            for node in self.get_children(node):
                get_items(node)

        if not tags:
            return
        elif isinstance(tags, str):
            tags = (tags,)

        if not item:
            items = []
            for child in self.get_children():
                get_items(child)
        else:
            items = [item]

        for item in items:
            _tags = list(self.item(item, 'tags'))
            for _tag in tags:
                if opt == 'add':
                    if _tag not in _tags:
                        _tags.append(_tag)
                elif opt == 'remove':
                    if _tag in _tags:
                        _tags.pop(_tags.index(_tag))
            self.item(item, tags=_tags)


class App(tk.Tk):
    def __init__(self):
        super().__init__()

        def button_press(event):
            self.anchor_x, self.anchor_y = event.x, event.y
            item = self.anchor_item = self.active_item = tv.identify('item', event.x, event.y)

            dw.geometry('0x0+0+0')
            dw.deiconify()
            self.bind('<Motion>', set_selected)

            if not item:
                if not event.state & 1 << 2:
                    tv.tags_reset()
                return

            if event.state & 1 << 2:
                if tv.tag_has('odd', item):
                    tv.tag_add('selected', item)
                    tv.tag_replace('odd', 'selected_odd', item)
                elif tv.tag_has('even', item):
                    tv.tag_add('selected', item)
                    tv.tag_replace('even', 'selected_even', item)
                elif tv.tag_has('selected_odd', item):
                    tv.tag_replace('selected_odd', 'odd', item)
                elif tv.tag_has('selected_even', item):
                    tv.tag_replace('selected_even', 'even', item)
            else:
                tv.tags_reset()
                tv.tag_add('selected', item)
                if tv.tag_has('odd', item):
                    tv.tag_replace('odd', 'selected_odd', item)
                elif tv.tag_has('even', item):
                    tv.tag_replace('even', 'selected_even', item)

        def button_release(_):
            dw.withdraw()
            self.unbind('<Motion>')

            for item in self.selected_items:
                if tv.tag_has('odd', item) or tv.tag_has('even', item):
                    tv.tag_remove(('selected', '_selected'), item)
                else:
                    tv.tag_replace('_selected', 'selected')

        def get_selected(event):
            selected_items = []
            window_y = int(self.geometry().rsplit('+', 1)[-1])
            titlebar_height = tv.winfo_rooty() - window_y

            start = dw.winfo_rooty() - titlebar_height - window_y
            end = start + dw.winfo_height()

            while start < end:
                start += 1
                node = tv.identify('item', event.x, start)
                if not node or node in selected_items:
                    continue
                selected_items.append(node)

            return sorted(selected_items)

        def set_selected(event):
            def set_row_colors():
                items = self.selected_items = get_selected(event)

                for item in items:
                    if tv.tag_has('selected', item):
                        if item == self.anchor_item:
                            continue

                        if tv.tag_has('selected_odd', item):
                            tv.tag_replace('selected_odd', 'odd', item)
                            tv.tag_add('_selected', item)
                        elif tv.tag_has('selected_even', item):
                            tv.tag_replace('selected_even', 'even', item)
                            tv.tag_add('_selected', item)

                    elif tv.tag_has('odd', item):
                        tv.tag_replace('odd', 'selected_odd', item)
                        tv.tag_add('_selected', item)
                    elif tv.tag_has('even', item):
                        tv.tag_replace('even', 'selected_even', item)
                        tv.tag_add('_selected', item)

                for item in tv.tag_has('_selected'):
                    if item not in items:
                        tv.tag_remove('_selected', item)
                        if tv.tag_has('odd', item):
                            tv.tag_replace('odd', 'selected_odd', item)
                        elif tv.tag_has('even', item):
                            tv.tag_replace('even', 'selected_even', item)
                        elif tv.tag_has('selected_odd', item):
                            tv.tag_replace('selected_odd', 'odd', item)
                        elif tv.tag_has('selected_even', item):
                            tv.tag_replace('selected_even', 'even', item)

            root_x = self.winfo_rootx()
            if event.x < self.anchor_x:
                width = self.anchor_x - event.x
                coord_x = root_x + event.x
            else:
                width = event.x - self.anchor_x
                coord_x = root_x + self.anchor_x

            if coord_x+width > root_x+self.winfo_width():
                width -= (coord_x+width)-(root_x+self.winfo_width())
            elif self.winfo_pointerx() < root_x:
                width -= (root_x - self.winfo_pointerx())
                coord_x = root_x

            root_y = self.winfo_rooty()
            if event.y < self.anchor_y:
                height = self.anchor_y - event.y
                coord_y = root_y + event.y
            else:
                height = event.y - self.anchor_y
                coord_y = root_y + self.anchor_y

            if coord_y+height > root_y+self.winfo_height():
                height -= (coord_y+height)-(root_y+self.winfo_height())
            elif self.winfo_pointery() < root_y + linespace:
                height -= (root_y - self.winfo_pointery() + linespace)
                coord_y = root_y + linespace
                if height < 0:
                    height = tv.winfo_rooty() + self.anchor_y

            dw.geometry(f'{width}x{height}+{coord_x}+{coord_y}')

            set_row_colors()

        def print_selected_items(_):
            print(sorted(tv.tag_has('selected_odd') + tv.tag_has('selected_even')))

        dw = tk.Toplevel(self)
        dw.wait_visibility(self)
        dw.withdraw()
        dw.config(bg='#00aaff')
        dw.overrideredirect(True)
        dw.wm_attributes('-alpha', 0.3)
        dw.wm_attributes("-topmost", True)

        tv = Treeview(self)
        button = ttk.Button(self, text='Get Selected Items')

        style = self.style = ttk.Style()
        style.map("Treeview", foreground=tv.fixed_map("foreground"), background=tv.fixed_map("background"))

        tv.heading('#0', text='Name')
        tv.tag_configure('odd', background='#ffffff')
        tv.tag_configure('even', background='#aaaaaa')
        tv.tag_configure('selected_odd', background='#b0eab2')
        tv.tag_configure('selected_even', background='#25a625')

        color_tag = 'odd'
        for idx in range(0, 4):
            # Populating the tree with test data.
            color_tag = 'even' if color_tag == 'odd' else 'odd'
            tv.insert('', idx, f'!{idx}', text=f'Item {idx+1}', open=1, tags=(color_tag,))
            color_tag = 'even' if color_tag == 'odd' else 'odd'
            iid = f'!{idx}_!{0}'
            tv.insert(f'!{idx}', '0', iid, text=f'Menu {idx+1}', open=1, tags=(color_tag,))
            for i in range(0, 5):
                color_tag = 'even' if color_tag == 'odd' else 'odd'
                tv.insert(iid, i, f'{iid}_!{i}', text=f'Sub item {i+1}', tags=(color_tag,))

            color_tag = 'even' if color_tag == 'odd' else 'odd'
            tv.insert(iid, 5, f'{iid}_!{5}', text=f'Another Menu {idx+1}', open=1, tags=(color_tag,))
            iid = f'{iid}_!{5}'
            for i in range(0, 3):
                color_tag = 'even' if color_tag == 'odd' else 'odd'
                tv.insert(iid, i, f'{iid}_!{i}', text=f'Sub item {i+1}', tags=(color_tag,))

        self.title('Treeview Demo')
        self.geometry('275x650+3000+250')
        self.rowconfigure(0, weight=1)
        self.columnconfigure(0, weight=1)
        self.update_idletasks()

        self.active_item = None
        self.selected_items = []

        tv.config(selectmode="none")
        tv.grid(sticky='NSEW')

        button.grid()

        font = tkfont.nametofont('TkTextFont')
        linespace = font.metrics('linespace') + 5

        button.bind('<Button-1>', print_selected_items)

        self.bind('<Escape>', tv.tags_reset)
        self.bind('<Button-1>', button_press)
        self.bind('<ButtonRelease-1>', button_release)


def main():
    app = App()
    app.mainloop()


if __name__ == '__main__':
    main()