Range Sum of BST

class Solution:
    def rangeSumBST(self, root: Optional[TreeNode], low: int, high: int) -> int:

        if not root:
            return 0

        count = 0

        # if root.val <= low: won't work here
        if root.val < low:
            count += self.rangeSumBST(root.right, low, high)
        # if root.val >= high: won't work here
        elif root.val > high:
            count += self.rangeSumBST(root.left, low, high)
        else:
            count += root.val
            count += self.rangeSumBST(root.left, low, high)
            count += self.rangeSumBST(root.right, low, high)

        return count