Binary Tree Level Order Traversal II LeetCode solution in Python

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class Solution:
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    def levelOrderBottom(self, root: Optional[TreeNode]) -> List[List[int]]:
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        def dfs(node, level, result):
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            if not node:
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                return
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            if level >= len(result):
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                result.append([])
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            result[level].append(node.val)
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            dfs(node.left, level + 1, result)
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            dfs(node.right, level + 1, result)
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        result = []
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        dfs(root, 0, result)
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        return result[::-1]