Here's the basic HTML+JS+CSS way to make them if your original structure is or can be UL / LI lists. Just in case you wanted to know HOW one worked.

<script>
function toggle(obj) {
    obj.parentNode.className = (obj.parentNode.className=='li-open') ?
+ 'li-closed' : 'li-open';
    return false;
}
</script>
<style type="text/css">
ul.dtree li.li-open   ul { display: block; }
ul.dtree li.li-closed ul { display: none; }
</style>
<ul class=dtree>
    <li class=li-closed>
        <div class="leaf" onClick="toggle(this)">Item</div>
        <ul>
            <li>Item 2</li>
            <li>Item 3</li>
        </ul>
    </li>
</ul>
[download]

BTW, I make my ul/li lists in perl and HTML::Template so nyaaah! ;)

This is task for javascript + CSS, not for perl
Upd: but HTML-PopupTreeSelect makes it

Tree::Simple::View should give you want you are looking for, the only thing is that you need to use Tree::Simple objects. This page contains a number of examples of the DHTML output, as well as the code used to create that output.

I just commented in your more recent node regarding this as well. I think you might find many of my Tree modules useful. Let me know if you are interested and have any questions.