서브메뉴 추가 방법은 어떻게 될까요?

<?php
                $menu_datas = get_menu_db(0, true);
                $gnb_zindex = 999; // gnb_1dli z-index 값 설정용
                $i = 0;
                foreach( $menu_datas as $row ){
                    if( empty($row) ) continue;
                    $add_class = (isset($row['sub']) && $row['sub']) ? 'gnb_al_li_plus' : '';
                ?>
                <li>
                    <a href="<?php echo $row['me_link']; ?>" target="_<?php echo $row['me_target']; ?>"><?php echo $row['me_name'] ?></a>
                    <?php
                    $k = 0;
                    foreach( (array) $row['sub'] as $row2 ){

                        if( empty($row2) ) continue; 

                        if($k == 0)
                            echo '<span class="bg"><i class="ion-ios-plus-empty visible-xs"></i></span><ul class="sub-nav">'.PHP_EOL;
                    ?>
                        <li><a href="<?php echo $row2['me_link']; ?>" target="_<?php echo $row2['me_target']; ?>"><?php echo $row2['me_name'] ?></a></li>
                    <?php
                    $k++;
                    }   //end foreach $row2

                    if($k > 0)
                        echo '</ul>'.PHP_EOL;
                    ?>
                </li>
           
                <?php
                $i++;
                }   //end foreach $row

                if ($i == 0) {  ?>
                    <li class="gnb_empty">메뉴 준비 중입니다.<?php if ($is_admin) { ?> <a href="<?php echo G5_ADMIN_URL; ?>/menu_list.php">관리자모드 &gt; 환경설정 &gt; 메뉴설정</a>에서 설정하실 수 있습니다.<?php } ?></li>
                <?php } ?>
                <!-- 추가메뉴-->
               <li> <a data-html = 'true' class="fixed" data-toggle="popover"  data-placement="bottom"  data-content="<iframe  width=100% frameborder=0  style='height:500px;width:280px'  scrolling='auto'  SRC='주소'></iframe>" data-trigger="hover"><font size="" color="yellow">추가메뉴</font></a>
                
                     
                     </li>