Merge Header - GridView/DataGrid

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public partial class _Default : System.Web.UI.Page 
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            GridView_Merge_Header.DataSource = GenerateDataSet();
            GridView_Merge_Header.DataBind();
        }
    }

    private DataSet GenerateDataSet()
    {
        DataSet ds= new DataSet("test");
        ds.ReadXml(HttpRuntime.AppDomainAppPath + "/Employee.xml");
        return ds;
    }
    protected void GridView_Merge_Header_RowCreated(object sender, GridViewRowEventArgs e)
    {
        if (e.Row.RowType == DataControlRowType.Header)
        {                    
            //Build custom header.
            GridView oGridView = (GridView)sender;
            GridViewRow oGridViewRow = new GridViewRow(0, 0, DataControlRowType.Header, DataControlRowState.Insert);
            TableCell oTableCell = new TableCell();

            //Add Department
            oTableCell.Text = "Department";
            oTableCell.ColumnSpan = 2;
            oGridViewRow.Cells.Add(oTableCell);

            //Add Employee
            oTableCell = new TableCell();
            oTableCell.Text = "Employee";
            oTableCell.ColumnSpan = 3;
            oGridViewRow.Cells.Add(oTableCell);

            oGridView.Controls[0].Controls.AddAt(0, oGridViewRow);
        }
    }
}