add screen set to group

Hi
I have a user menu add to my user id.
user menu contains 2 groups A and B .
B has 2 screen sets added, when i tried to add another screen set under B by selecting + symbol which is beside B, it is getting added at parent level.
but not under group B.
i wanted to add ascreen set under B along with those 2 existing screen sets.
help me.