from django.contrib import admin
from django.db import models
from mptttreewidget.widget import MpttTreeWidget

class ProductAdmin(admin.ModelAdmin):
  formfield_overrides = {
    models.ManyToManyField: { 'widget': MpttTreeWidget }
  }

from django.contrib import admin
from django import forms
from mptttreewidget.widget import MpttTreeWidget

class ProductForm(forms.ModelForm)
  categories = forms.ModelMultipleChoiceField(required=False, queryset=Category.objects.all(), widget=MpttTreeWidget)

  class Meta:
      model = Product

class ProductAdmin(admin.ModelAdmin):
  form = ProductForm