Easy Recursive Python3 solution faster than 99%
```\nclass Solution:\n    def rangeSumBST(self, root: TreeNode, low: int, high: int) -> int:\n        s = 0\n        def explore(root, low, high):\n            
```\nclass Solution:\n    def rangeSumBST(self, root: TreeNode, low: int, high: int) -> int:\n        s = 0\n        def explore(root, low, high):\n            nonlocal s\n            if low<=root.val<=high:\n                s += root.val\n            if root.left and low<root.val:\n                explore(root.left, low, high)\n            if root.right and high>=root.val:\n                explore(root.right, low, high)\n        explore(root, low, high)\n        return s\n\t
['Recursion', 'Python', 'Python3']