You can also drag from a Finder window (on the Mac) but it can only import one level of folders, so make sure you re-create the rest of your folder structure as bins first.
I had to import 5 days of 4-track audio recordings and it just kept bundling the tracks from the same day in a single folder, which was too bad, since they were all named 1.wav, 2.wav etc.
So I made bins for the days and just dragged all the file folders from each day into the day bins from the Finder window. Presto!