Mage2\Catalog\Module::registerAdminMenu PHP Method

    public function registerAdminMenu()
    {
        $adminUserMenu = ['catalog' => ['label' => 'Catalog', 'route' => '#', 'submenu' => ['category' => ['label' => 'Category', 'route' => 'admin.category.index'], 'product' => ['label' => 'Products', 'route' => 'admin.product.index']]]];
        AdminMenu::registerMenu('mage2-catalog', $adminUserMenu);
    }