Included among chromatic button accordions is what chromatic button accordion developed in Russia in the early 20th century and named after the 11th-century bard Boyan?
Chromatic button accordion:  The bass-side keyboard is usually the Stradella system or one of the various free-bass systems. Included among chromatic button accordions are the Russian bayan and Schrammel accordion. Bayan (accordion): The bayan (Russian: бая́н ; ] ) is a type of chromatic button accordion developed in Russia in the early 20th century and named after the 11th-century bard Boyan.
bayan