Python-сообщество

class Category(models.Model):
    slug = models.SlugField()
    parent = models.ForeignKey('self', blank=True, null=True)

root_categories = Category.objects.filter(parent=None)

{% for root_category in root_categories %}
- {{root_category}}
{% for sub_category in root_category.category_set.all %}
--- {{sub_category}}
{% endfor %}
{% endfor %}