How to change the case-sensitive grouping in WinForms GridGroupingControl?

#region Custom Categorizer class

//defines custom categorizer
public class CustomCategorizer : Syncfusion.Grouping.IGroupByColumnCategorizer
{
    public static string GetCategory(string key)
    {
        return key;
    }

    #region IGroupByColumnCategorizer Members
    public object GetGroupByCategoryKey(SortColumnDescriptor column, bool isForeignKey, Record record)
    {
        return GetCategory(record.GetValue(column.Name).ToString());
    }

    public int CompareCategoryKey(SortColumnDescriptor column, bool isForeignKey, object category, Record record)
    {
        return string.Compare(GetCategory(record.GetValue(column.Name).ToString()), (string)category, true);
    }
    #endregion
}

#Region "Custom Categorizer class"

'defines custom categorizer
Public Class CustomCategorizer
    Implements Syncfusion.Grouping.IGroupByColumnCategorizer
    Public Shared Function GetCategory(ByVal key As String) As String
        Return key
    End Function

     #Region "IGroupByColumnCategorizer Members"
     Public Function GetGroupByCategoryKey(ByVal column As SortColumnDescriptor, ByVal isForeignKey As Boolean, ByVal record As Record) As Object
         Return GetCategory(record.GetValue(column.Name).ToString())
     End Function

     Public Function CompareCategoryKey(ByVal column As SortColumnDescriptor, ByVal isForeignKey As Boolean, ByVal category As Object, ByVal record As Record) As Integer
         Return String.Compare(GetCategory(record.GetValue(column.Name).ToString()), CStr(category), True)
     End Function
     #End Region
End Class