How to group the values in parameter drop-down

<div id="viewer"></div>
<script>
    $("#viewer").boldReportViewer({
              beforeParameterAdd: "onBeforeParameterAdd"
        });
</script>
</html>

<script type="text/javascript">
    var $targetTag = $('#' + args.containerId);
    function onBeforeParameterAdd(args) {
        if (args.customProperties != null && args.parameterModel.Name == "Products") {
            var $targetTag = $('#' + args.containerId);

            if ($("#" + args.parameterModel.ControlId + "_popup_wrapper").length > 0) {
                $("#" + args.parameterModel.ControlId + "_popup_wrapper").remove();
            }

            var $paramMultiValuedropdown = ej.buildTag("select.e-rptviewer-multivalue", "", {}, { 'id': args.parameterModel.ControlId + '_element', 'type': 'text', 'data-sf-name': args.parameterModel.Name });

            $targetTag.append($paramMultiValuedropdown);
            $paramMultiValuedropdown.ejDropDownList({
                cssClass: 'e-js e-reportviewer-param e-rptviewer-drpdown',
                width: "100%",
                dataSource: args.parameterModel.DataSource,
                change: function (sender) {
                    var paramId = (this._id.indexOf("Param") < 0) ? sender.target.id : this._id;
                    var targetTag = $('#' + paramId);

                    var updateParam = {
                        name: '',
                        labels: [],
                        values: []
                    };

                    updateParam.name = targetTag.attr('data-sf-name');
                    updateParam.labels.push(sender.text);
                    updateParam.values.push(sender.text);

                    $('#Viewer').data('boldReportViewer').updateParameter(updateParam);
                },
                fields: { text: "Name", category: "ProductCategoryID" }, allowGrouping: true, enableloadOnDemand: false
            });
            args.handled = true;
        }
    }
</script>
</html>