Make subcategories in template script

I really need help with a script i have bought, the script has some categories, but i also need sub categories, so i added an extra field in the table traffic_categories. The original traffic_categories has id and category, but i have added sub_id also, so if the category is a main category it has 0 in sub_id, but if the category is a sub category it has the main category id in the sub_id field.. Simple..

The problem is the script hava an advanced template system i can´t figure out how works. Here is the script that gets the categories from mysql:

$result = mysql_query('SELECT category FROM traffic_categories WHERE sub_id = 0 ORDER BY category ASC;');
$iCat=2;
$CONF['categories'] = array(); $TMPL['cats'] = '';
while(list($TMPL['cat']) = mysql_fetch_row($result)) {
    $TMPL['cath'] = str_replace(' ', '+', $TMPL['cat']);
    $TMPL['cats'] .= base::do_skin('menu/cats');
    $CONF['categories'][] = $TMPL['cat'];

        $TMPL['last'] = $iCat++ % 4 === 0 ? ' last' : '';
}

PHP:

and here is cats.html:

<div class="one-fourth{$last}">
    <h5><a href="/cat/{$cath}">{$cat}</a></h5>
    <ul class="categoryList">
        Here i want the subcategories--><li> - <a href=""></a></li>
    </ul>
</div>

HTML:

and in my frontpage.html where the categories will be showed is just {$cats}.

So if someone please can help me show the subcategories inside the list in cats.html where is have written "Here i want the subcategories-->", then i will be really glad, thanks.