Sylius\Bundle\TaxonomyBundle\Form\Type\TaxonChoiceType::buildView PHP Method

    public function buildView(FormView $view, FormInterface $form, array $options)
    {
        /** @var ChoiceView $choice */
        foreach ($view->vars['choices'] as $choice) {
            $choice->label = str_repeat('— ', $choice->data->getLevel()) . $choice->label;
        }
    }