# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def createBinaryTree(self, descriptions: List[List[int]]) -> Optional[TreeNode]:
        graph = {}
        children = set()

        def build(root: Optional[TreeNode]) -> None:
            children = graph.get(root.val)

            if children:
                for child, flag in children:
                    if flag:
                        root.left = TreeNode(child)
                    else:
                        root.right = TreeNode(child)

                if root.left:
                    build(root.left)
                if root.right:
                    build(root.right)

        for parent, child, flag in descriptions:
            if parent in graph:
                graph[parent].append((child, flag))
            else:
                graph[parent] = [(child, flag)]
            children.add(child)

        root = None

        for parent, _, _ in descriptions:
            if parent not in children:
                root = parent

        head = TreeNode(root)
        build(head)

        return head