private function registerDefaultPostTypes()
    {
        $this->registerPostType('post', [
            'labels'        => ['name' => 'Posts', 'singular' => 'Post',],
            'hierarchical'  => false,
            'show_ui'       => true,
            'icon'          => 'fa fa-pencil',
            'menu_position' => 10,
            '_built_in'     => true,
        ]);

        $this->registerPostType('page', [
            'labels'        => ['name' => 'Pages', 'singular' => 'Page',],
            'hierarchical'  => true,
            'show_ui'       => true,
            'icon'          => 'fa fa-file',
            'menu_position' => 11,
            '_built_in'     => true,
        ]);
    }