console
<html>
<head>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap-select@1.13.9/dist/css/bootstrap-select.min.css" />
</head>
<body>
<select class="selectpicker" multiple data-actions-box="true">
<option>Mustard</option>
<option>Ketchup</option>
<option>Relish</option>
</select>
</body>
<script src="https://cdn.jsdelivr.net/npm/bootstrap-select@1.13.9/dist/js/bootstrap-select.min.js"></script>
<script>
const picker = $('.selectpicker');
picker.on('loaded.bs.select', selectedFirst);
picker.on('change.bs.select', selectedFirst);
function selectedFirst () {
$(this).find('option:selected').prependTo(this);
$(this).selectpicker('refresh');
console.log(picker.val())
}
</script>
</html>