SO jQuery Fiddle

Test Fiddle mainly for SO Questions jQuery 1.4.3, UI 1.8.5

by Nick Craver

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.5/themes/ui-lightness/jquery-ui.css">
<ul>  
<li id="1" parent="0"><a href="#">1</a></li>  
    <li id="2" parent="0"><a href="#"> + </a><a href="#">2</a>  
        <ul parent="2">  
            <li id="23" parent="2"><a href="#">2.1</a></li>  
            <li id="50" parent="2"><a href="#"> + </a><a href="#">2.2</a>  
                <ul parent="50">  
                    <li id="123" parent="50"><a  href="#">2.50.1</a></li>  
                </ul>  
            </li>  
        </ul>  
    </li>
</ul>

CSS

ul ul { display: none; }

JavaScript

$("ul a:contains( + )").click(function() {
  $(this).siblings("ul").slideToggle();
});