How to get option group of selected item on .chosen().change()

by Can

HTML

<link rel="stylesheet" href="http://lysik.pl/public/chosen.css">
<script src="http://lysik.pl/public/chosen.jquery.js"></script>
<select class="chosen" style="width:300px;">
    <optgroup label="fruit">
        <option value="1">apples</option>
        <option value="2">pears</option>
    </optgroup>
    <optgroup label="veg">
        <option value="3">neeps</option>
        <option value="4">tatties</option>
    </optgroup>
    <optgroup label="omnivore">
        <option value="5">bear</option>
        <option value="6">rats</option>
    </optgroup>
</select>

JavaScript

$('.chosen').chosen().change(
    function (evt) {
        var label = $(this.options[this.selectedIndex]).closest('optgroup').prop('label');
        alert(label);
});