嵌套Regroups - Django

# models.py
class Category(models.Model):
    name = models.CharField(max_length=100)
    parent = models.ForeignKey('self', null=True, blank=True, related_name='children', on_delete=models.CASCADE)

class Product(models.Model):
    name = models.CharField(max_length=100)
    category = models.ForeignKey(Category, on_delete=models.CASCADE)

# views.py
def product_list(request):
    categories = Category.objects.all()
    return render(request, 'product_list.html', {'categories': categories})

<!-- product_list.html -->
{% regroup categories by parent as parent_groups %}
<ul>
{% for parent_group in parent_groups %}
    <li>{{ parent_group.grouper.name }}
        {% regroup parent_group.list by name as child_groups %}
        <ul>
        {% for child_group in child_groups %}
            <li>{{ child_group.grouper }}
                <ul>
                {% for product in child_group.list %}
                    <li>{{ product.name }}</li>
                {% endfor %}
                </ul>
            </li>
        {% endfor %}
        </ul>
    </li>
{% endfor %}
</ul>

categories = Category.objects.all().order_by('parent__name', 'name')