Binary Tree Postorder Traversal

My Solution:

# Recursive Approach

# 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

def postorderTraversal(root: Optional[TreeNode]) -> List[int]:
    if not root:
        return []

    return [*postorderTraversal(root.left), *postorderTraversal(root.right), root.val]