Shop By Departments menu

functions.php

<?php
function media_center_department_nav_menu(){
	$department_nav_menu = '';

    $department_nav_menu .= '<ul class="dropdown-menu">';
    $department_nav_menu .=  wp_list_categories(
      array(
          'title_li'     => '', 
          'hide_empty'   => 1 , 
          'taxonomy'     => 'product_cat',
          'hierarchical' => 1 ,
          'echo'         => 0 ,
      )
    );
    $department_nav_menu .= '</ul>';

    return $department_nav_menu;
}