How many levels of recursion are in your source? Can that be defined?
If you have, for example 3 levels, you would need to use the folder table three times and join them using a 0 to 1 or 0 to N relationship. This way the parent folders do not need to have child folders, but you would pre-define the number of levels you would go down to. You would join a child folder by parent_folder_id to the parent folder folder_id.
Once you define that, then the mapping should be obvious.
If you're still not sure what to do please tell me when you want to do a gotomeeting. I could do one this evening (tomorrow morning your time).