Alex137a1,
<!DOCTYPE HTML>
<html>
<head>
<title></title>
<meta charset="utf-8" />
<style type="text/css">
li ul {
display: none;
}
</style>
<script src="https://code.jquery.com/jquery-latest.js"></script>
<script type="text/javascript">
$(function () {
$('ul').prev('a').on('click', function (event) {
event.preventDefault();
$(this).next("ul").slideToggle() ;
});
});
</script>
</head>
<body>
<nav class="navigation">
<ul>
<li><a href="">item 1</a>
<ul>
<li><a href="">sub item 1-a</a></li>
<li><a href="">sub item 1-b</a></li>
</ul>
</li>
<li><a href="">item 2</a>
<ul>
<li><a href="">sub item 2-a</a></li>
<li><a href="">sub item 2-b</a></li>
</ul>
</li>
</ul>
</nav>
</body>
</html>