show categories with sub categories list before product on shop page

woo-show-sub-categories.php

// show categories with sub categories list before product on shop page
function understrap_woocommerce_before_shop_loop() {

    echo '<ul class="product-cats">';

        woocommerce_output_product_categories();

    echo '</ul>';

    $term_id = get_queried_object()->term_id;

    if($term_id) {

        echo '<ul class="product-cats">';

            woocommerce_output_product_categories(array(

                    'parent_id'     => $term_id,
            ));

        echo '</ul>';
    }
}

add_action('woocommerce_before_shop_loop', 'understrap_woocommerce_before_shop_loop', 8);