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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def flatten(self, d=None):
 """Flatten tree structure to a one level dictionary. Args: d (dict, optional):
 output dictionary to update Returns: dict: Node.name -> Node. The returned dictionary includes the current Node and all its children. """

        if d is None:
            d = {}
        if self.name is not None:
            d[self.name] = self
        for child in self.children:
            child.flatten(d=d)
        return d