Complex sentence: His piano music forms the bulk of his creative output, with a concerto, a concertino, twelve sonatas, and a variety of other pieces written for the instrument, virtuosic pieces as well as pedagogical and amateur-level compositions.
Split into simpler sentences: His piano music forms the bulk of his creative output, with a concerto, a concertino, twelve sonatas, and a variety of other pieces written for the instrument. These were virtuosic pieces as well as pedagogical and amateur-level compositions.