DefaultAdminFormTestHooks.php

<?php

declare (strict_types=1);
namespace Drupal\default_admin_form_test\Hook;

use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Hook\Attribute\Hook;

/**
 * Hook implementations for default_admin_form_test.
 */
class DefaultAdminFormTestHooks {
  
  /**
   * Implements hook_form_BASE_FORM_ID_alter() for node_form.
   *
   * Entity forms are allowed to set #tree, and some contributed ones do, so
   * the node form stands in for them here.
   */
  public function formNodeFormAlter(array &$form, FormStateInterface $form_state) : void {
    $form['#tree'] = TRUE;
  }

}