VocabularyStorage.php

<?php

namespace Drupal\taxonomy;

use Drupal\Core\Config\Entity\ConfigEntityStorage;

/**
 * Defines a storage handler class for taxonomy vocabularies.
 */
class VocabularyStorage extends ConfigEntityStorage implements VocabularyStorageInterface {
    
    /**
     * {@inheritdoc}
     */
    public function getToplevelTids($vids) {
        $tids = \Drupal::entityQuery('taxonomy_term')->accessCheck(TRUE)
            ->condition('vid', $vids, 'IN')
            ->condition('parent.target_id', 0)
            ->execute();
        return array_values($tids);
    }

}