code: def shift_ordering_up(cls, parent_id, position, db_session=None, *args, **kwargs):
          
          db_session = get_db_session(db_session)
          query = db_session.query(cls.model)
          query = query.filter(cls.model.parent_id == parent_id)
          query = query.filter(cls.model.ordering >= position)
          query.update(
              {cls.model.ordering: cls.model.ordering + 1}, synchronize_session=False
          )
          db_session.flush()
docs: Shifts ordering to "open a gap" for node insertion,
          begins the shift from given position
  
          :param parent_id:
          :param position:
          :param db_session:
          :return: