Sorting tree wrt top level items

def sort_top_level_items(self, key):
        """Sorting tree wrt top level items"""
        self.save_expanded_state()
        items = sorted([self.takeTopLevelItem(0)
                        for index in range(self.topLevelItemCount())], key=key)
        for index, item in enumerate(items):
            self.insertTopLevelItem(index, item)
        self.restore_expanded_state()