Sorry for asking such a basic question...
How do I add a new branch on Object Window in CS?
There are many weapons of different material, such as Iron, Ebony, and Silver.
If I want to add a new classification branch of weapon( for example: plastic ), what should I do?
Thanks in advance.

I think, but I'm not entirely shore, that when you add a new item to the list it will create a new branch equal to the file path. So if you want your branches to be nice and organised you will have to add your custom objects to a long file path by putting files inside files.

Wow... I'll try it later, thanks!

This should have been asked in the CS area but Create a folder using windows explorer, under weapons named plastic or what ever and put your weapon nifs in that and when you create a new weapon and draw a Nif from that it will add the Branch to the tree that you want. Also don't forget to put the do the same for and under textures.