bootstrap多选项选择框在joomla中不起作用

I use bootstrap selectpicker to select multiple options. Code is:

<select id="product_parent_id" class="selectpicker" size="1" name="product_parent_id[]"  multiple data-selected-text-format="count">
    <?php 
    foreach ($result_cat as $key => $cat) {
        $cat_name='';
        if($cat->category_parent_id!=0) {
            $cnt=0;
            $cat_name='';
            $r_cat=$cat->category_parent_id;

            do {
                $cnt++;
                $qur='SELECT category_parent_id FROM #__virtuemart_category_categories WHERE id='.$r_cat;
                $db->setQuery($qur);
                $r_cat=$db->loadResult();
            } while($r_cat!=0);


            for($i=0;$i<$cnt;$i++) {
                $cat_name=$cat_name.'-';
            }
            $cat_name=$cat_name.$cat->category_name;
        } else {
            $cat_name=$cat->category_name;
        }

        $sel_c='';
        if(in_array((string)$cat->id,$sel_cat_arr)) {
            $sel_c='selected="true"';
        }

        ?>
        <option value="<?php echo $cat->id;?>" <?php echo $sel_c;?>><?php echo $cat_name;?></option>

    <?php
    }
    ?>
</select>

I downloaded bootstrap-selectpicker.zip

I use cdn: bootstrap-select.css,bootstrap-select.js

The selectpicker works in normal html page but in joomla select box it is not displayed. I found conflicts, but didn't get the solution.

Check if this works,

<?php 
                foreach ($result_cat as $key => $cat) {


                    $cat_name='';
                    if($cat->category_parent_id!=0)
                    {
                        $cnt=0;
                        $cat_name='';
                        $r_cat=$cat->category_parent_id;


                        do{
                            $cnt++;
                            $qur='SELECT category_parent_id FROM #__virtuemart_category_categories WHERE id='.$r_cat;
                            $db->setQuery($qur);
                            $r_cat=$db->loadResult();

                        }while($r_cat!=0);


                        for($i=0;$i<$cnt;$i++)
                        {
                            $cat_name=$cat_name.'-';
                        }
                        $cat_name=$cat_name.$cat->category_name;
                    }
                    else
                    {
                        $cat_name=$cat->category_name;
                    }
                    $sel_c='';
                    if(in_array((string)$cat->id,$sel_cat_arr))
                    {
                        $sel_c='selected="true"';
                    }
        echo '<option   value=\"'.$cat->id.'">'.$cat_name.'</option>';

                ?>