<link href="//maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<link href="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.6-rc.0/css/select2.min.css" rel="stylesheet" />
<div class="container">
<select id="country" multiple>
<option disabled></option>
<option value="AK">Alaska</option>
<option value="HI">Hawaii</option>
<option value="CA">California</option>
<option value="NV">Nevada</option>
<option value="OR">Oregon</option>
<option value="WA">Washington</option>
<option value="AZ">Arizona</option>
<option value="CO">Colorado</option>
<option value="ID">Idaho</option>
<option value="MT">Montana</option>
<option value="NE">Nebraska</option>
<option value="NM">New Mexico</option>
<option value="ND">North Dakota</option>
<option value="UT">Utah</option>
<option value="WY">Wyoming</option>
<option value="AL">Alabama</option>
<option value="AR">Arkansas</option>
<option value="IL">Illinois</option>
<option value="IA">Iowa</option>
<option value="KS">Kansas</option>
<option value="KY">Kentucky</option>
<option value="LA">Louisiana</option>
<option value="MN">Minnesota</option>
<option value="MS">Mississippi</option>
<option value="MO">Missouri</option>
<option value="OK">Oklahoma</option>
<option value="SD">South Dakota</option>
<option value="TX">Texas</option>