This code will return the full category tree with all the classes needed for the customization.
<div class="block block-leftnav">
<div class="block-title">
<strong><?php echo $this->__('Browse Category') ?></strong>
</div>
<div class="block-content">
<ul>
<?php foreach ($this->getStoreCategories() as $_category): ?>
<?php if($_category->name!=""): ?>
<?php echo $this->drawItem($_category) ?>
<?php endif ?>
<?php endforeach ?>
</ul>
</div>
</div>