вывод mptt дерева в админке

gistfile1.py

def __unicode__(self):
        return '%s%s' % (' --- ' * self.level, self.title)

class MPTTMeta:
    order_insertion_by = ['title']

class Meta:
    verbose_name = _('category')
    verbose_name_plural = _('categories')
    ordering = ['tree_id', 'lft']