Thank you for writing.
You can achieve this behavior through the CellClick event. You have to check whether the user has clicked on a group row and collapse/expand the row. Here is a code snippet which demonstrates this:
sender, GridViewCellEventArgs e)
e.Row.IsExpanded = !e.Row.IsExpanded;
I hope this will be useful for you. Should you have further questions, I would be glad to help.
All the best,
the Telerik team