protected function _construct()
{
$this->addColumn('term_id', ['label' => '']);
$this->addColumn('reference_term', ['label' => __('Reference Term')]);
$this->addColumn('values', ['label' => __('Expansion terms')]);
$this->_addAfter = false;
$this->_addButtonLabel = __('Add Expansion');
parent::_construct();
}