protected function _prepareForm()
    {
        /** @var \Magento\Framework\Data\Form $form */
        $form = $this->_formFactory->create(
            ['data' => ['id' => 'edit_form', 'action' => $this->getData('action')]]
        );

        $thesaurusTypes = [
            ['value' => ThesaurusInterface::TYPE_SYNONYM, 'label' => __('Synonym')],
            ['value' => ThesaurusInterface::TYPE_EXPANSION, 'label' => __('Expansion')],
        ];

        $fieldset = $form->addFieldset('base_fieldset', ['legend' => __('Type')]);

        $fieldset->addField(
            'type',
            'select',
            [
                'name' => 'type',
                'label' => __('Thesaurus Type'),
                'title' => __('Thesaurus Type'),
                'values' => $thesaurusTypes,
            ]
        );

        $form->setUseContainer(true);
        $this->setForm($form);

        return parent::_prepareForm();
    }