Creating subheader in gridview

<asp:gridview id="GridView1"    class="attr"> runat="server" autogeneratecolumns=        class="attrv">"false" datasourceid="SqlDataSource1"
 onrowdatabound="GridView1_RowDataBound">
 <columns>
  <asp:boundfield datafield=            class="attrv">"ProductID" headertext="ProductID" />
  <asp:boundfield datafield=            class="attrv">"Name" headertext="Name" />
  <asp:boundfield datafield=            class="attrv">"Subcategory" headertext="Subcategory" />
 </columns>
</asp:gridview>
<asp:sqldatasource id=    class="attrv">"SqlDataSource1" runat="server"        class="attr"> connectionstring="<%$
            ConnectionStrings:AdventureWorksConnectionString %>"
 selectcommand="SELECT P.*, PS.[Name]
    AS [Subcategory] FROM [Production].[Product] AS P INNER JOIN [Production].[ProductSubcategory]
    AS PS ON PS.[ProductSubcategoryID] = P.[ProductSubcategoryID] ORDER BY P.[ReorderPoint],
    P.[Name]">
</asp:sqldatasource>

CODE-BEHIND 

private string m_subcategory = String.Empty;

protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
 GridViewRow gvr = e.Row;

 switch (gvr.RowType)
 {
  case DataControlRowType.DataRow:
  {
   DataRowView drv = gvr.DataItem as DataRowView;

   string subcategory = drv["subcategory"].ToString();

   if (!subcategory.Equals(m_subcategory))
   {
    GridViewRow row = new GridViewRow(0, 0, DataControlRowType.DataRow, DataControlRowState.Normal);
    TableCell cell = new TableCell();
    cell.BackColor = Color.Red;
    cell.ForeColor = Color.White;
    cell.ColumnSpan = GridView1.Columns.Count;
    cell.HorizontalAlign = HorizontalAlign.Center;
    cell.Text = subcategory;
    row.Cells.Add(cell);

    GridView1.Controls[0].Controls.AddAt(GridView1.Controls[0].Controls.Count - 1, row);

    m_subcategory = subcategory;
   }


   break;
  }
 }
}