Blender Pie Menu>Submenu

import bpy
from bpy.types import Menu

class VIEW3D_PIE_submenu(bpy.types.Menu):
    bl_label = 'Pie Submenu'
    bl_idname = 'view3d_pie_template.submenu'

    def draw(self, context):
        layout = self.layout

        layout.label("This is a submenu")
        layout.operator("render.render")
        layout.operator("render.render")
        layout.operator("render.render")

class VIEW3D_PIE_template(Menu):
    bl_label = "Some Pie Menu"

    def draw(self, context):
        layout = self.layout
        pie = layout.menu_pie()
        pie.operator("mesh.primitive_cube_add")
        pie.operator("mesh.primitive_cube_add")
        pie.operator("mesh.primitive_cube_add")
        pie.operator("mesh.primitive_cube_add")
        pie.operator("mesh.primitive_cube_add")
        pie.operator("mesh.primitive_cube_add")
        pie.operator("mesh.primitive_cube_add")
        pie.operator("mesh.primitive_cube_add")
        pie.separator()
        pie.separator()
        gap = pie.column()
        gap.separator()
        gap.separator()
        gap.separator()
        gap.separator()
        gap.separator()
        gap.separator()
        gap.separator()
        menu = gap.box()
        menu.scale_x = 2.5
        col = menu.column()
        col.scale_y = 1.5
        col.operator("mesh.primitive_monkey_add")
        col.operator("mesh.primitive_monkey_add")
        menu.box().menu('view3d_pie_template.submenu', icon='RIGHTARROW')

def register():
    bpy.utils.register_class(VIEW3D_PIE_template)
    bpy.utils.register_class(VIEW3D_PIE_submenu)

def unregister():
    bpy.utils.unregister_class(VIEW3D_PIE_template)
    bpy.utils.unregister_class(VIEW3D_PIE_submenu)

if __name__ == "__main__":
    register()

    bpy.ops.wm.call_menu_pie(name="VIEW3D_PIE_template")