private void Page_Load(object sender, System.EventArgs e)
    {
      DataSet myDataSet = new DataSet();
      
      myDataSet.Tables.Add(MakeDataTable("test"));
      myDataSet.Merge(MakeDataTable("test"));
      DataGrid1.DataSource = myDataSet;
      DataGrid1.DataBind();
    }

    private DataTable MakeDataTable(string name)
    {
      
      System.Data.DataTable myDataTable = new DataTable(name);
      
      DataColumn myDataColumn;
      
      DataRow myDataRow;
 
       
      myDataColumn = new DataColumn();
      myDataColumn.DataType = typeof(System.Int32);
      myDataColumn.ColumnName = "id";
      myDataTable.Columns.Add(myDataColumn);
 
      
      myDataColumn = new DataColumn();
      myDataColumn.DataType = System.Type.GetType("System.String");
      myDataColumn.ColumnName = "ParentItem";

      myDataTable.Columns.Add(myDataColumn);
 
      
      for (int i = 0; i<= 2; i++)
      {
        myDataRow = myDataTable.NewRow();
        myDataRow["id"] = i;
        myDataRow["ParentItem"] = "ParentItem " + i;
        myDataTable.Rows.Add(myDataRow);
      }
      return myDataTable;
    }