text: class Solution:
      def rangeSumBST(self, root: TreeNode, low: int, high: int) -> int:
          if not root:
              return 0
          if root.val < low or root.val > high:
              currSum = 0
          else:
              currSum = root.val
          if root.val > low:
              currSum += self.rangeSumBST(root.left, low, high)
          if root.val < high:
              currSum += self.rangeSumBST(root.right, low, high)
          return currSum
  