This is the aria "Ombra mai fù" from Handel's opera "Xerxes" (Serse), a love song of the King of Persia, Xerxes, to a tree. It is one of Handel's best-known melodies and is often referred to simply as "Handel's Largo". The arrangement for double bass and piano (or harp) comes with two piano parts: one in A major to accompany the double bass in solo tuning and one in G major to accompany the double bass in orchestral tuning.