Can anyone help me figure out why my code does not generate [[1]] at OJ?

My code generates the correct result on my local IDE.

Thanks in advance.

Input: {1}

Output: 1

Expected: [[1]]

```
def levelOrderBottom(self, root):
res = []
if root == None:
return res
else:
level = []
q = collections.deque([])
q.append(root)
curChild=1
nexChild=0
while q:
n = q.popleft()
curChild-=1
print n.val
level.append(n.val)
if n.left!=None:
q.append(n.left)
nexChild+=1
if n.right!=None:
q.append(n.right)
nexChild+=1
if curChild==0:
curChild = nexChild
nexChild = 0
res.append(list(level))
del level[:]
res.reverse()
return res
```