leetcode Binary Tree Level Order Traversal python

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
def levelOrder(self, root):
"""
:type root: TreeNode
:rtype: List[List[int]]
"""
res=[]

if root is None:
return res
level=0

rs=self.levelOrderRe(root,level,res)

return rs
def levelOrderRe(self,tree,level,res):
if tree is None:
return res

if len(res) < level+1:
res.append([])
res[level].append(tree.val)
res=self.levelOrderRe(tree.left,level+1,res)
res=self.levelOrderRe(tree.right,level+1,res)
return res