How to combine xml using two xml input ?

private void GenerateXML()
{
    string strCon = ConfigurationManager.ConnectionStrings["CConnectionString"].ToString();\\Get the connection string form database
    SqlConnection conn = new SqlConnection(strCon);
    conn.Open();
    SqlDataAdapter da = null;
    DataSet ds = new DataSet();
    try
    {
        string strSql = "SELECT [Desc], [Title], [Number] FROM [TableName]";
        da = new SqlDataAdapter(strSql, conn);
        da.Fill(ds, "SampleTable");

	ds.WriteXml("C:\\Test.xml");
        
    }
    catch (Exception ex)
    {
        lblError.Text = "Error!! <br>+" + ex.Message.ToString();
    }
    finally
    {
        ds.Dispose();
        da.Dispose();
        conn.Close();
        conn.Dispose();
    }
}