Here's my solution in Python for Binary Tree Level Order Traversal:

```
class Solution:
traversal = []
depth = -1
# @param root, a tree node
# @return a list of lists of integers
def levelOrder(self, root):
if root == None:
return Solution.traversal
Solution.depth += 1
if Solution.depth == len(Solution.traversal):
Solution.traversal.append([root.val])
else:
(Solution.traversal[Solution.depth]).append(root.val)
self.levelOrder(root.left)
self.levelOrder(root.right)
Solution.depth -= 1
return Solution.traversal
```

For the test case {1, 2}, OJ will produce output [[1, 1], [2]], but my own machine gives the correct answer [[1], [2]]. Did I understand something wrong here or is there a bug in OJ?