# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    '''
    Time Complexity: O(n)
    Space Complexity: O(w)
    Where, n is number of nodes in the tree, w is maximum width of the tree.
    Simple BFS level order traversal problem.
    '''
    def maxLevelSum(self, root: Optional[TreeNode]) -> int:
        maxValue = root.val
        maxLevel = 1
        level = 1
        nodes = [root]

        while nodes:
            childNodes = []
            value = 0
            for node in nodes:
                if node.left:
                    childNodes.append(node.left)
                if node.right:
                    childNodes.append(node.right)
                value += node.val
            if value > maxValue:
                maxLevel = level
                maxValue = value
            nodes = childNodes
            level += 1
        
        return maxLevel