Display data in alphabetical order indexed by the alphabet using Repeater in ASP.Net

HTML

<asp:Repeater ID="rptParent" runat="server" OnItemDataBound="rptParent_OnItemDataBound">
    <ItemTemplate>
        <asp:Label ID="lblProductAbbr" Text='<%# Eval("Abbr") %>' runat="server" />
        <asp:Repeater ID="rptChild" runat="server">
            <ItemTemplate>
                <table>
                    <tr>
                        <td align="left">
                            <asp:Label ID="lblProductAbbr" Text='<%# Eval("ProductName") %>' runat="server" />
                        </td>
                    </tr>
                </table>
            </ItemTemplate>
        </asp:Repeater>
    </ItemTemplate>
</asp:Repeater>

Namesapace

using System.Configuration;
using System.Data.SqlClient;
using System.Data;

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        Populate("SELECT DISTINCT SUBSTRING(ProductName,1,1) AS Abbr FROM dbo.Products", this.rptParent);
    }
}

protected void rptParent_OnItemDataBound(object sender, RepeaterItemEventArgs e)
{
    if (e.Item.ItemType == ListItemType.Item || e.Item.ItemType == ListItemType.AlternatingItem)
    {
        Repeater rpt = e.Item.FindControl("rptChild") as Repeater;
        Populate(string.Format("SELECT DISTINCT ProductName FROM dbo.Products WHERE ProductName LIKE '{0}%'", (e.Item.FindControl("lblProductAbbr") as Label).Text), rpt);
    }

}

private void Populate(string query, Repeater rpt)
{
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection _cn = new SqlConnection(constr))
    {
        using (SqlCommand _cmd = new SqlCommand(query, _cn))
        {
            using (SqlDataAdapter da = new SqlDataAdapter(_cmd))
            {
                DataSet ds = new DataSet();
                da.Fill(ds);
                rpt.DataSource = ds;
                rpt.DataBind();
            }
        }
    }
}

Screenshot