I am trying to build a form that contain parent category select,but it is a nested table,here is the datatable structure:

CREATE TABLE [dbo].[cms_categories](
    [id] [int] IDENTITY(1,1) NOT NULL,
    [parent_id] [int] NULL,
    [title] [varchar](255) NULL,
    [name] [varchar](255) NULL,
    [alias] [varchar](255) NULL,
    [image] [varchar](255) NULL,
    [description] [text] NULL,
    [published] [tinyint] NULL,
    [checked_out] [int] NULL,
    [checked_out_time] [datetime] NULL,
    [ordering] [int] NULL,
 CONSTRAINT [PK_cms_categories] PRIMARY KEY CLUSTERED
(
    [id] ASC
)WITH (PAD_INDEX  = OFF, IGNORE_DUP_KEY = OFF) ON [PRIMARY]
) 

 In my controller,I use the following code:

 ViewData Class

public class CategoryNewViewData
    {
        public List ParentCategory { get; set; }
    }

 Controller Action

        public ActionResult AddForm()
        {
            CategoryNewViewData Category = new CategoryNewViewData();
            ViewData["ParentCategory"] = new SelectList(repository.Categories.ToList(), "id", "name");
            return View();
        }

And View Page Operation

<%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master" AutoEventWireup="true" CodeBehind="AddForm.aspx.cs" Inherits="CMS.Views.Category.AddForm" %>
<%@ Import Namespace="CMS.Models" %>
<asp:Content ID="Content1" ContentPlaceHolderID="MainContent" runat="server">
<h2>Add Content Category</h2>
<p>Please fill in the following blanks</p>

<form method="post" action="/Category/Add">
    <label for="CategoryName">Category Name:</label>
    <%= Html.TextBox("CategoryName") %>
    <br />
    <label for="ParentCategory">Parent Category：</label>
    <%= Html.DropDownList("ParentCategory")%>
    <br />
    <%= Html.SubmitButton("submit", "Add") %>
</form>
</asp:Content> 

But we got a problem,Because the top level category's id is 0(zero),and the SelectOption is "Top Level",and this option dosn't stored int the database(and i don't wanna add a record to database)

 So,How could we add an option to that list like(<option value="0">Top Level</option>)

Anybody who can give me a hand?

thanks a lot