Add One Row to Tree LeetCode solution in Python

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class Solution:
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    def addOneRow(self, root: TreeNode, v: int, d: int) -> TreeNode:
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        if d == 1:
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            return TreeNode(v, root, None)
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        elif d == 2:
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            root.left = TreeNode(v, root.left, None)
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            root.right = TreeNode(v, None, root.right)
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        else:
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            if root.left:
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                self.addOneRow(root.left, v, d - 1)
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            if root.right:
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                self.addOneRow(root.right, v, d - 1)
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        return root