How to use the superscript option for the text box cell in the WinForms GridGroupingControl?

void gridGroupingControl1_QueryCellStyleInfo(object sender, Syncfusion.Windows.Forms.Grid.Grouping.GridTableCellStyleInfoEventArgs e)
{
    if (e.TableCellIdentity.Column != null && e.TableCellIdentity.Column.Name == "City"
        && e.TableCellIdentity.DisplayElement.Kind == Syncfusion.Grouping.DisplayElementKind.Record)
    {
        string rtf = @"{\rtf1\ansi\ansicpg1252\deff0\deflang1033{\fonttbl{\f0\fnil\fcharset0 Microsoft Sans Serif;}} \viewkind4\uc1\pard\f0\fs17 Syncfusion\up15 2\up0\par}";
        //declare celltype as RichTextBox
        e.Style.CellType = GridCellTypeName.RichText;
        e.Style.CellValue = rtf;
    }
}

Private Sub gridGroupingControl1_QueryCellStyleInfo(ByVal sender As Object, ByVal e As Syncfusion.Windows.Forms.Grid.Grouping.GridTableCellStyleInfoEventArgs)
    If e.TableCellIdentity.Column IsNot Nothing AndAlso e.TableCellIdentity.Column.Name = "City" AndAlso e.TableCellIdentity.DisplayElement.Kind Is Syncfusion.Grouping.DisplayElementKind.Record Then
        Dim rtf As String = "{\rtf1\ansi\ansicpg1252\deff0\deflang1033{\fonttbl{\f0\fnil\fcharset0 Microsoft Sans Serif;}} \viewkind4\uc1\pard\f0\fs17 Syncfusion\up15 2\up0\par}"
        'declare celltype as RichTextBox
        e.Style.CellType = GridCellTypeName.RichText
        e.Style.CellValue = rtf
    End If
End Sub