Display category and subcategory hierarchical

This is what I'm trying to achieve:

So the result should be like this:

<ul class="product-categories">
    <li class="cat-item cat-item-18 current-cat">
        <a href="/product-category/autumn-winter-2014-2015/">Autumn-Winter 2014-2015</a>
        <ul class="product-subcategories">
            <li class="cat-item cat-item-20"><a href="/product-category/autumn-winter-2014-2015/abrigo/">abrigo</a></li>
        </ul>
    </li>
    <li class="cat-item cat-item-19"><a href="/product-category/silk-collection/">Silk collection</a></li>
</ul>

The problem is that right now, categories and subcategories are displaying the same way:

<ul class="product-categories">
    <li class="cat-item cat-item-20"><a href="/product-category/autumn-winter-2014-2015/abrigo/">abrigo</a></li>
    <li class="cat-item cat-item-18 current-cat"><a href="/product-category/autumn-winter-2014-2015/">Autumn-Winter 2014-2015</a></li>
    <li class="cat-item cat-item-19"><a href="/product-category/silk-collection/">Silk collection</a></li>
</ul>

I'm using this code on woocommerce to output the menu:

        global $wp_query, $post, $woocommerce;

        $this->current_cat = false;
        $this->cat_ancestors = array();

        if ( is_tax('product_cat') ) {

            $this->current_cat = $wp_query->queried_object;
            $this->cat_ancestors = get_ancestors( $this->current_cat->term_id, 'product_cat' );

        } elseif ( is_singular('product') ) {

            $product_category = wc_get_product_terms( $post->ID, 'product_cat', array( 'orderby' => 'parent' ) );

            if ( $product_category ) {
                $this->current_cat   = end( $product_category );
                $this->cat_ancestors = get_ancestors( $this->current_cat->term_id, 'product_cat' );
            }

        }

        include_once( $woocommerce->plugin_path() . '/classes/walkers/class-product-cat-list-walker.php' );

        $cat_args['walker']             = new WC_Product_Cat_List_Walker;
        $cat_args['title_li']           = '';
        $cat_args['show_children_only'] = ( isset( $instance['show_children_only'] ) && $instance['show_children_only'] ) ? 1 : 0;
        $cat_args['pad_counts']         = 1;
        $cat_args['show_option_none']   = __('No product categories exist.', 'woocommerce' );
        $cat_args['current_category']   = ( $this->current_cat ) ? $this->current_cat->term_id : '';
        $cat_args['current_category_ancestors'] = $this->cat_ancestors;

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

        wp_list_categories( apply_filters( 'woocommerce_product_categories_widget_args', $cat_args ) );

        echo '</ul>';

Any help on how to do this?