get_categories listing foreach with children

My code for loop of categories

<?php
$categories = get_categories('hide_empty=1&exclude=1&orderby=slug&order=ASC');
foreach ($categories as $category) {
    echo '<li class="cat-item cat-item-'.$category->cat_ID.'">';
    echo '<a href="'.site_url().'/category/'.$category->slug.'">';
    echo $category->cat_name;
    echo "</a>";
    echo ' ('.$category->category_count.')';
    echo '</li>';
}
?>

Preview the code above:

<ul>
    <li><a href="#">Category one</a></li>
    <li><a href="#">Category two</a></li>
    <li><a href="#">CHILDREN OF Category third</a></li>
    <li><a href="#">Category third</a></li>
</ul>

I would like to stay:

<ul>
    <li><a href="#">Category one</a><span class="description">...</span>
        <ul class="children">
            <li><a href="#">Children primary of Category one</a></li>
            <li><a href="#">Children second of Category one</a></li>
            <li><a href="#">Children third of Category one</a></li>
        </ul>
    </li>
    <li><a href="#">Category two</a><span class="description">...</span></li>
    <li><a href="#">Category third</a><span class="description">...</span>
        <ul class="children">
            <li><a href="#">Children primary of Category third</a></li>
            <li><a href="#">Children second of Category third</a></li>
            <li><a href="#">Children third of Category third</a></li>
        </ul>
    </li>
</ul>

understand?