SO fiddle

Test Fiddle mainly for SO Questions

by Nick Craver

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.4/themes/overcast/jquery-ui.css">
<ul id="tree">
    <li class="parents" id="parent_1"><a href="#">Parent 1</a>
        <ul class="child_list">
            <li class="child"><a href="#">Child 1</a></li>
            <li class="child"><a href="#">Child 2</a></li>
            <li class="child"><a href="#">Child 3</a></li>
        </ul>
    </li>
    <li class="parents" id="parent_2"><a href="#">Parent 2</a>
        <ul class="child_list">
            <li class="child"><a href="#">Child 1</a></li>
            <li class="child"><a href="#">Child 2</a></li>
            <li class="child"><a href="#">Child 3</a></li>
        </ul>
    </li>
</ul>

CSS

.child_list {
    display: none;
}

JavaScript

$(function(){
    $(".parents").click(function(){
        // Open list
        $(this).find("ul").slideDown();

        // Remember opened list
        //$.cookie('tree', '#' + this.id);

        // Cycle through all lists
        $(this).siblings().find("ul").slideUp();
    });
});