# 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 inorderTraversal(self, root: TreeNode) -> List[int]:
to_ret = []
def inorder(root):
if not root:
return
inorder(root.left)
to_ret.append(root.val)
inorder(root.right)
inorder(root)
return to_ret