Bootstrap select live search error

Mhon bantuanya agan2 ini saya coba menggunakan bootstrap select live search cuman kok datanya tidak keluar ya padahal tidak terdapat error pada console log

code is

          <select class="form-control selectpicker" data-live-search="true" id="kd_brng" name="kd">
            <?php
            if ($_SESSION['kelas'] == "PBO") {
              $kelas = "brng_pbo";
            }elseif ($_SESSION['kelas'] == "TKR") {
              $kelas = "brng_tkr";
            }else{
              $kelas = "brng_tsm";
            }

            $data_ctn = $db->select("$kelas", "kd_brng,nm_brng", null , "nm_brng ASC", null);

            if(is_array($data_ctn))
            {
              foreach ($data_ctn as $ctn)
              {
                ?>
                <option value='<?= $ctn['nm_brng'];?>' data-tokens="<?= $ctn['nm_brng'];?>"><?= $ctn['nm_brng'];?></option>
              <?php }}?>
            </select>

ada sarankah errornya dmn ??