```
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
from collections import deque
class Solution(object):
def levelOrderBottom(self, root):
"""
:type root: TreeNode
:rtype: List[List[int]]
"""
results = []
if not root :
return results
queue = deque([root])
while queue:
level = []
for i in range(len(queue)):
front = queue.popleft()
level.append(front.val)
if front.left:
queue.append(front.left)
if front.right:
queue.append(front.right)
results.append(level)
return results[::-1]
```