在Symfony2表单上显示选定的字段单选按钮

Question

I'm trying to make a radio button list from the entity Category as shown below the code.

The database structure is like this for the category table:

id_category, name, level, parent_id, child_id

I would only want the radio button to only appear on the last category with no child_id on it. For example:

Apparels -> Men -> T-shirt

I only want the radio button to appear on T-shirt, how can I do that? I've tried querying but it doesn't show the other Parent Category.

Is there a correct way to do this in Symfony2?

public function buildForm(FormBuilderInterface $builder, array $options){

    $builder->add('productLanguage', new ProductLanguageType()) //embed another form
            ->add('id_seller','text')
            ->add('tag', 'text')
            ->add('hot', 'checkbox')
            ->add('featured', 'checkbox')
            ->add('new', 'checkbox')
            ->add('id_category', 'entity', array(
                   'class' => 'ProductBundle:ProductCategory',
                   'property' => 'name',
                   'multiple' => false,
                   'expanded' => true
                  )
                 )
            ->add('id_condition', 'entity', array(
                   'class' => 'ProductBundle:ProductCondition',
                   'property' => 'cond'
                  )
                 )
            ->add('Add', 'submit');

}