Increasing Order Search Tree LeetCode solution in Python

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class Solution:
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    def increasingBST(self, node: TreeNode) -> TreeNode:
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        dummy = tail = TreeNode()
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        while node is not None:
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            if node.left is not None:
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                predecessor = node.left
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                while predecessor.right is not None:
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                    predecessor = predecessor.right
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                predecessor.right = node
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                left, node.left = node.left, None
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                node = left
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            else:
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                tail.right = tail = node
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                node = node.right
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        return dummy.right