code: def __get_deep_dependent_item_set(self, item, item_set) -> None:
          
          if not item in item_set:
              item_set.add(item)
              with self.__dependency_tree_lock:
                  for dependent in self.get_dependent_items(item):
                      self.__get_deep_dependent_item_set(dependent, item_set)
docs: Return the list of data items containing data that directly depends on data in this item.