Grouping does not end. I want to start a new group

I am working on an exercise in which I have to group certain rows. But it is giving trouble. A new group is not starting but the rows are added to the same group. Please help
It works fine for the first time with (selection.rows.group function).
But when user click again, new group is not created, instead the rows are added in the same group in another outline level
But i want seperate groups. Please Help.
I have attached my xls file