code: def filter_objects_by_section(self, rels, section):
          
  
          subtree = section.get_descendants(include_self=True)
          kwargs_list = [{'%s__in' % rel.field.name: subtree} for rel in rels]
          q = Q(**kwargs_list[0])
          for kwargs in kwargs_list[1:]:
              q |= Q(**kwargs)
          return self.get_manager(get_item_model_class()).filter(q).distinct()
docs: Build a queryset containing all objects in the section subtree.