For convenience reasons Banshee is distributed with a unmodified binary executable of Bison. 
Bison is not integrated into Banshee in any way and is used as a tool during the build process. 
Bison is licensed under GPL which you must respect if you integrate it into your application or 
modify its source. You may download the Bison source and view the license terms on "https://www.gnu.org/software/bison". 