DropDownList with OptionGroup

<%@ Page Language="C#" AutoEventWireup="true" Codebehind="TestRequiredFieldValidator.aspx.cs"
    Inherits="TestWebApplication.TestRequiredFieldValidator" MasterPageFile="~/Site1.Master"
    Title="TestRequiredFieldValidator" %>

<%@ Register TagPrefix="ddlb" Assembly="OptionDropDownList" Namespace="OptionDropDownList" %>

<asp:Content ID="Content1" ContentPlaceHolderID="MainContent" runat="Server">
    <div>
        <ddlb:OptionGroupSelect ID="OptionGroupSelect1" runat="server" Width="300px">
            <ddlb:OptionGroupItem ID="OptionGroupItem0" runat="server" Value="0" Text="-- Select --"
                Selected="true" />
            <ddlb:OptionGroupItem ID="OptionGroupItem1" runat="server" Value="1" Text="UNE" OptionGroup="Odd" />
            <ddlb:OptionGroupItem ID="OptionGroupItem2" runat="server" Value="2" Text="TWO" OptionGroup="Even" />
            <ddlb:OptionGroupItem ID="OptionGroupItem3" runat="server" Value="3" Text="TREE"
                OptionGroup="Odd" />
            <ddlb:OptionGroupItem ID="OptionGroupItem4" runat="server" Value="4" Text="FOUR"
                OptionGroup="Even" />
        </ddlb:OptionGroupSelect>
        <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ErrorMessage="Please choose a value"
            ControlToValidate="OptionGroupSelect1" InitialValue="0">*</asp:RequiredFieldValidator><br />
        <br />
        <asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Submit" />
        <br />
        <br />
        <asp:ValidationSummary ID="ValidationSummary1" runat="server" />
    </div>
</asp:Content>