107. Binary Tree Level Order Traversal II

        res=[]
        if not root:
            return res
        queue=collections.deque()
        queue.append(root)
        while queue:
            level=[]
            for i in range(len(queue)):
                node=queue.popleft()
                level.append(node.val)
                if node.left:
                    queue.append(node.left)
                if node.right:
                    queue.append(node.right)
            res.append(level)
        return res.reverse() 

class Solution:
    
    def __init__(self):
        self.traverse=[]
        
    def levelOrderBottom(self, root):
        """
        :type root: TreeNode
        :rtype: List[List[int]]
        """
        if not root:
            return []
        level = [root]
        self.traverse.append([node.val for node in level])
        self.traverse_helper(level)
        
        return self.traverse[::-1]
    
    def traverse_helper(self,level):
        
        if not level:
            return 
        queue = []
        for node in level:
            if node.left:
                queue.append(node.left)
            if node.right:
                queue.append(node.right)
        if not queue:
            return
        
        self.traverse.append([node.val for node in queue])
        self.print_traverse(queue)
        self.traverse_helper(queue)
    
    def print_traverse(self,level):
        for node in level:
            print(node.val)