Double-decker buses I saw in Europe...

MAN 2 axle bus in Berlin, Germany

MAN 3 axle bus in Berlin, Germany (It has 2 stairs - one behind
the driver, one at the back)

Another MAN 3 axle bus in Berlin, Germany

A double-decker in Rome, Italy. (I dunno the brand/model of the
bus. But I know Route 110 is operated by ATAC (Rome's transport
operator) and is catered for tourists.)

Another double-decker in front of Rome Termini

Volvo 3 axle bus in Copenhagen, Denmark (It looks like a Berlin
bus because it's yellow too.)

Another Volvo 3 axle bus in Copenhagen, Denmark