First of all get 30 discs, and put 2 aside for now! Then, figure out a unit you would like to use. I used the writable part of the discs! But pay attention, if you don't want an equilateral triangle, you're gonna need a different unit!
Now, glue the discs together. There are several kinds of glues, please use one that is gel based. I have tried other ones and unfortunately other stronger glue types will erode your discs... trust me, I tried them all!
Try to first glue together the layers, and then position them together for the tree.
If your glue is all dried up, you will need some fishing line. It is advised to tie the discs together through their holes. Once you put the paint onto it, it will dry up and serve as another type of glue, that'll help hold all these CDs together! Then, cover all the holes with some tape. (I didn't want the paint to get on the other side, seeing that that way it will be still seen that these are discs.)
Finally it is time to paint! I advise you use spray paint, that is more likely to stick.
Let it dry for 24 hours, so the strong paint odour evaporates.
In the meanwhile prepare the two CDs you put aside, and paint them with brown color paint.
If our tree is all dried up, attach the trunk to the end. You may force the fishing line from behind as well (where the CDs meet or next to the holes. Just a drop of gel glue is more than enough!).
You may use some more fishing line to be able to hang up your tree on your wall or window.