according to the front fender it's a 1928 BMW. Note that the cylinders are at a 90 degree angle, flat-twin engine design.
Invented by M. Goventosa de Udine in 1931, the one wheeled motorcycle. Little is known about de Udine (not shown), even if he was the sole inventor. What is known is that this one wheeled motorcycle could reach speeds of 150km/hr.
Wilkinson Bros BMW R75/6 Cafe Racer