https://leetcode.com/problems/search-in-a-binary-search-tree/
class Solution:
def searchBST(self, root, val):
"""
:type root: TreeNode
:type val: int
:rtype: TreeNode
"""
res = root
while res:
if res.val == val:
return res
elif res.val<val:
res = res.right
else:
res = res.left
return None