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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 to_strings(self):
 """ Convert the expansion node to a list of expansion strings. :return: a list of expansion strings that represent the leaf nodes of the expansion tree. :rtype: list[union[str, unicode]] """

        result = []

        if not self.expansions:
            result.append(self.name)
        else:
            for expansion in self.expansions:
                result.extend('{}.{}'.format(self.name, es) for es in expansion.to_strings())

        return result