/**
  * {@inheritdoc}
  */
 public function buildForm(FormBuilderInterface $builder, array $options)
 {
     $categoryClassName = $this->categoryRepository->getClassName();
     $builder->add('trees', 'oro_entity_identifier', ['class' => $categoryClassName, 'required' => false, 'mapped' => false, 'multiple' => true]);
     $builder->add('categories', 'oro_entity_identifier', ['class' => $categoryClassName, 'required' => true, 'mapped' => true, 'multiple' => true]);
 }