def kthSmallest(self, root: Optional[TreeNode], k: int) -> int:
        """
        if not root: 
            return
        cur = root
        stack = [root]

        while stack: 
            while cur: 
                stack.append(cur)
                cur = cur.left
            cur = stack.pop()
            if k == 1: 
                return cur.val
            cur = cur.right
            k -= 1
        """