WordPress: Adding a plugin in an existing menu structure

I have a an existing set of WooCommerce plugins, the plugins that allow a user to enter product details, some of you may be familiar. I've made a new plugin that I'd like to add as a sub-menu in the existing menu structure.

Class WC_Batch_Category_Import_Plugin {

static $instance;

public function __construct() {
    add_action( 'admin_menu', array( $this, 'plugin_menu' ), 99 );
}

public function plugin_menu() {

        $hook = add_submenu_page(
            'edit.php?post_type=product',
            'Batch Category Import',
            'Batch Category Import',
            'manage_woocommerce',
            'batch-category-import'
        );

        add_action( "load-$hook" );
    }

    public static function get_instance() {
        if ( ! isset( self::$instance ) ) {
            self::$instance = new self();
        }
    return self::$instance;
        }
    }


add_action( 'plugins_loaded', __construct() () {
    WC_Batch_Category_Import_Plugin::get_instance();
} );

I have the following code, although with this code in the plugin, the menu is not being displayed. Does anyone know why? Thanks

via Chebli Mohamed