<link href="//cdn.bootcss.com/select2/3.5.4/select2.min.css" rel="stylesheet"/>

<script src="//cdn.bootcss.com/jquery/1.7.1/jquery.min.js"></script>

<script src="//cdn.bootcss.com/select2/3.5.4/select2.min.js"></script>

<script>

$(document).ready(function() {

   $("#e2").select2({

    placeholder: "请选择...",

    allowClear: true

    });

    $("#e2_2").select2({

        placeholder: "请选择..."

    });

});

</script>

<p>

    <select id="e2" style="width:300px">

    <option></option>

    <optgroup label="Alaskan/Hawaiian Time Zone">

        <option value="AK">Alaska</option>

        <option value="HI">Hawaii</option>

    </optgroup>

    <optgroup label="Pacific Time Zone">