Kth Smallest Element in a BST

1# Definition for a binary tree node.
2# class TreeNode:
3#     def __init__(self, val=0, left=None, right=None):
4#         self.val = val
5#         self.left = left
6#         self.right = right
7class Solution:
8    def kthSmallest(self, root: Optional[TreeNode], k: int) -> int:
9        
10        def tree_to_list(root) -> list:
11            if not root:
12                return []
13
14            return tree_to_list(root.right) + [root.val] + tree_to_list(root.left)
15        
16        tree_list = tree_to_list(root)
17        return tree_list[-k]