Multiple playlists created through import

[syyoung]

I initially imported a MAME set that had Sega Model 2 games as a subcategory with games populated in the list.  I tried later to import more Model 2 games from a separate folder, and it imported them into a separate playlist also called Sega Model 2.  How can I combine these two lists?  Do I need to delete one and add the items manually to the other?  I'm confused on this.  Thanks!