如何将自定义属性创建为其他属性的子项作为下拉目录输入类型

I'm trying to create something like part finder (product finder). I was thinking to edit layered navigation. So now I have drop-boxes instead of list using this code for

app/design/frontend/default/carpoint/template/catalog/layer/filter.phtml

<select onchange="setLocation(this.value)">
<?php $count = 0; ?>
 <?php foreach ($this->getItems() as $_item): ?> 
 <?php $count++; ?>
 <?php if($count == 1): ?>
<option value='' disabled selected style='display:none;'>Choose <?php echo $attribute_code = $_item->getFilter()->getName();?> </option> 
<?php endif; ?>
<option <?php if ($_item->getCount() > 0): ?> value="<?php echo $this->urlEscape($_item->getUrl()) ?>">
<?php echo $_item->getLabel() ?> <?php else: echo '>' . $_item->getLabel() ?> <?php endif; ?> (<?php echo $_item->getCount() ?>) </option>
<?php endforeach; ?> 
</select>

How can I edit custom attribute eg "Type" so he is associated with parent attribute eg "Brand". I something like this: