[Zope] Best way to go

Hi, I need to offer keywords to users to choose from to use to index documents. There will be so much keywords that the only way to present them in a proper way is probably through a tree view. Now, what would be the best way to make this: 1) create a 'tree' keyword python product and create zope management interfaces for that. Thus we've one product which keeps the keys internally 2) create a keyword product and build the tree in the ZODB as like you could build a hierarchy with folders 3) use plain folders for the keywords. I'm not sure which would be the best choice. Anybody who can give me some advice? Thanks in advance, Tom.