I Want to Do a multiple selector on ASPnet MVC

<div class="form-row">
                    <div class="form-group col-md-6">
                        <label asp-for="EmployeeId" class="control-label"></label>
                        @Html.DropDownListFor(m => m.EmployeeId, (SelectList)ViewBag.LineManager, "Select", new { @class = "form-control selectpicker" })
                        @Html.ValidationMessageFor(model => model.EmployeeId, "", new { @class = "text-danger" })
                    </div>
                </div>