code: def sort_top_level_items(self, key):
          
          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()
docs: Sorting tree wrt top level items