def _create_tree_space(self, target_tree_id, num_trees=1):
        qs = self._mptt_filter(tree_id__gt=target_tree_id)
        self._mptt_update(qs, tree_id=F(self.tree_id_attr) + num_trees)
        self.tree_model._mptt_track_tree_insertions(target_tree_id + 1, num_trees)
Creates space for a new tree by incrementing all tree ids
dataset/ETHPy150Open django-mptt/django-mptt/mptt/managers.py/TreeManager._create_tree_space