메뉴에 아코디언을 적용하려고 합니다

<nav id="gnb">
    <h2>메인메뉴</h2>
    <div class="gnb_wrap">
        <ul id="gnb_1dul">
            <li class="gnb_1dli gnb_mnal"><button type="button" class="gnb_menu_btn"><i class="fa fa-bars" aria-hidden="true"></i><span class="sound_only">전체메뉴열기</span></button></li>
            <?php
            $sql = " select *
                        from {$g5['menu_table']}
                        where me_use = '1'
                          and length(me_code) = '2'
                        order by me_order, me_id ";
            $result = sql_query($sql, false);
            $gnb_zindex = 999; // gnb_1dli z-index 값 설정용
            $menu_datas = array();

            for ($i=0; $row=sql_fetch_array($result); $i++) {
                $menu_datas[$i] = $row;

                $sql2 = " select *
                            from {$g5['menu_table']}
                            where me_use = '1'
                              and length(me_code) = '4'
                              and substring(me_code, 1, 2) = '{$row['me_code']}'
                            order by me_order, me_id ";
                $result2 = sql_query($sql2);
                for ($k=0; $row2=sql_fetch_array($result2); $k++) {
                    $menu_datas[$i]['sub'][$k] = $row2;
                }

            }

            $i = 0;
            foreach( $menu_datas as $row ){
                if( empty($row) ) continue;
            ?>
            <li class="gnb_1dli" style="z-index:<?php echo $gnb_zindex--; ?>">
                <a href="<?php echo $row['me_link']; ?>" target="_<?php echo $row['me_target']; ?>" class="gnb_1da"><?php echo $row['me_name'] ?><!--<img src="<?=G5_IMG_URL?>/menu_<?php echo $i ?>.png" />--></a>
                <?php
                $k = 0;
                foreach( (array) $row['sub'] as $row2 ){

                    if( empty($row2) ) continue;

                    if($k == 0)
                        echo '<span class="bg">하위분류</span><ul class="gnb_2dul">'.PHP_EOL;
                ?>
                    <li class="gnb_2dli"><a href="<?php echo $row2['me_link']; ?>" target="_<?php echo $row2['me_target']; ?>" class="gnb_2da"><?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 } ?>
        </ul>

        <div id="gnb_all">
            <h2>전체메뉴</h2>
            <ul class="gnb_al_ul">
                <?php

                $i = 0;
                foreach( $menu_datas as $row ){
                ?>
                <li class="gnb_al_li">
                    <a href="<?php echo $row['me_link']; ?>" target="_<?php echo $row['me_target']; ?>" class="gnb_al_a"><?php echo $row['me_name'] ?></a>
                    <?php
                    $k = 0;
                    foreach( (array) $row['sub'] as $row2 ){
                        if($k == 0)
                            echo '<ul>'.PHP_EOL;
                    ?>
                        <li><a href="<?php echo $row2['me_link']; ?>" target="_<?php echo $row2['me_target']; ?>"><i class="fa fa-caret-right" aria-hidden="true"></i> <?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) { ?> <br><a href="<?php echo G5_ADMIN_URL; ?>/menu_list.php">관리자모드 &gt; 환경설정 &gt; 메뉴설정</a>에서 설정하실 수 있습니다.<?php } ?></li>
                <?php } ?>
            </ul>
            <button type="button" class="gnb_close_btn"><i class="fa fa-times" aria-hidden="true"></i></button>
        </div>
    </div>
</nav>

<script>
$(function(){
    $(".gnb_1dli .bg").click(function(){
        var submenu = $(this).next(".gnb_2dul");

        // submenu 가 화면상에 보일때는 위로 보드랍게 접고 아니면 아래로 보드랍게 펼치기
        if( submenu.is(":visible") ){
            submenu.slideToggle();
        }else{
            submenu.stop().toggle(500);
        }
    });
});
</script>