class Solution:
def searchBST(self, root: TreeNode, val: int) -> TreeNode:
if root == None:
return
if val < root.val:
return self.searchBST(root.left, val) #注意加return,否则下层递归无法返回到本层
elif val > root.val:
return self.searchBST(root.right, val) #注意加return
else:
return root