Tony Biase did have his own criminal group, but it wasn't Cosa Nostra. He did have Cosa Nostra associates. Here's a couple links for more:

http://omahamagazine.com/tag/tony-biase/

http://law.justia.com/cases/federal/appellate-courts/F2/302/95/132186/

Here's the AmericanMafia piece Ivy mentioned:
http://americanmafia.com/Cities/Omaha.html