menu_example.php

function tachp_make_department_menu( $items, $args ) {

        global $wp;

        if ( 'main' != $args->menu->slug ) {
                return $items;
        }

        $terms = get_terms('Department', array(
                'orderby' => 'name',
                'hide_empty' => true,
                )
        );
        // what is the current page?
        $current_url = add_query_arg( array(), $wp->request );

        ob_start();
        ?>
        <li id="menu-item-dept-list" class="menu-item menu-item-type-custom menu-item-object-custom menu-item-dept-list>"><a href="#">By Department</a>
        <?php
        echo '<ul class="sub-menu">';
        foreach ( $terms as $a ) {
                                ?>
                        <?php
                        if ( 'departments/' . $a->slug == $current_url ) {
                                $current_classes = ' current-menu-item ';
                        } else {
                                $current_classes = '';
                        }
                                ?>
                         <li id="menu-item-dept-<?php echo $a->slug;
                ?>" class="menu-item menu-item-type-custom menu-item-object-custom menu-item-dept-<?php echo $a->slug; echo $current_classes;
                ?>"><a href="/departments/<?php echo $a->slug;
                ?>/"><?php echo $a->name;
                ?></a></li>
                        <?php

        }
        echo '</li></ul>';

        $contents = ob_get_contents();
        /*
         * find the first occurrence of "All Classes"
         * and put this list right after_title
        */
        $search = 'All Classes</a></li>';
        $replace = $search . $contents;
        $newstr = str_replace( $search, $replace, $items );

        ob_end_clean();

        return $newstr;
}
        add_action( 'wp_nav_menu_items', 'tachp_make_department_menu', 10, 2 );