code: def get_siblings(self):
          
          qset = get_result_class(self.__class__).objects.filter(
              depth=self.depth
          ).order_by(
              'path'
          )
          if self.depth > 1:
              # making sure the non-root nodes share a parent
              parentpath = self._get_basepath(self.path, self.depth - 1)
              qset = qset.filter(
                  path__range=self._get_children_path_interval(parentpath))
          return qset
docs: :returns: A queryset of all the node's siblings, including the node
              itself.