About addressbook group level

[xajh]

I want to have mutlti-level group , But only support two level group now . Help me , Very thanks .

Now group level like this:

Groupname
|-Group_1
|-Group_2
|_Group_3


I want to like this:

Groupname
|-Group_1
| |-Department_1
| |-Department_2
| |_Department_3
|-Group_2
| |-Department_1
| |-Department_2
| | |-SubGroup-1
| | |-SubGroup-2
| |_Department_3
.......