class Solution:
    def bstFromPreorder(self, preorder: List[int]) -> Optional[TreeNode]:
        if len(preorder) == 0:
            return None
        return TreeNode(
            val=preorder[0],
            left=self.bstFromPreorder([v for v in preorder if v < preorder[0]]),
            right=self.bstFromPreorder([v for v in preorder if v > preorder[0]]),
        )