how sort DropDownList items alphabetically asp.net

I am quite new In asp.net. Today I want to sort my drop down list. This is my controller of editing:

public ActionResult Edit(int? id)
        {
            if (id == null)
            {
                retu new HttpStatusCodeResult(HttpStatusCode.BadRequest);
            }
            User user = db.Users.Find(id);
            if (user == null)
            {
                retu HttpNotFound();
            }
            ViewBag.DefaultCustomerProjectId = new SelectList(db.CustomerProjects, "Id", "Name", user.DefaultCustomerProjectId);
            ViewBag.DefaultServiceId = new SelectList(db.Services, "Id", "Name", user.DefaultServiceId);
            ViewBag.CustomerId = new SelectList(db.Customers, "Id", "Name", user.CustomerId);
            retu View(user);
        }

And this is my edit view

@model TimeReportingLib.User
@{
    ViewBag.Title = "Edit";
}
<h2>Edit</h2>
@using (Html.BeginForm())
{
    @Html.AntiForgeryToken()

    <div class="form-horizontal">
        <h4>User</h4>
        <hr />
        @Html.ValidationSummary(true, "", new { @class = "text-danger" })
        @Html.HiddenFor(model => model.Id)
<div class="form-group">
            @Html.LabelFor(model => model.DefaultServiceId, "DefaultServiceId", htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.DropDownList("DefaultServiceId", null, htmlAttributes: new { @class = "form-control" })
                @Html.ValidationMessageFor(model => model.DefaultServiceId, "", new { @class = "text-danger" })
            </div>
        </div>

How can I sort my @Html.DropDownList alphabetically?