Change Category List in Sidebar to expandable

How do i go about changing the below code for the sidebar categories (i believe this is it), to only showing the parent category, and expandable if child categories exist?

<!-- sidebar menu (categories) -->
      <ul class="menu">
        <?php if(!get_arclite_option('jquery')):
          echo preg_replace('@\<li([^>]*)>\<a([^>]*)>(.*?)\<\/a>@i', '<li$1><a class="fadeThis"$2>$3</a>', wp_list_categories('show_count=0&echo=0&title_li='));
         else:
          echo preg_replace('@\<li([^>]*)>\<a([^>]*)>(.*?)\<\/a> \(\<a ([^>]*) ([^>]*)>(.*?)\<\/a>\)@i', '<li $1><a class="fadeThis"$2>$3</a><a class="rss tip" $4></a>', wp_list_categories('show_count=0&echo=0&title_li=&feed=XML'));
         endif;
         if (function_exists('xili_language_list')) xili_language_list(); ?>
      </ul>
      <!-- /sidebar menu -->