In Germany there was a tradition of writing songs about Christmas trees and the most famous is "O Tannenbaum" which was written by the organist and teacher Ernst Anschütz (1780-1861) who was based in Leipzig. He used an old folk melody called "Lauriger Horatius" for his carol. The same melody has proven a popular one for many different songs (often with a patriotic character) including "Maryland, My Maryland" the official state song of the US State, and the socialist anthem "The Red Flag" - here is an arrangement of the piece for piano suitable for playing or accompanying The Red Flag.
The Christmas Carol can be downloaded as PDF sheet music, midi or mp3 files using the links in the left hand menu. In addition the following sheet music allows the piece to be played by a range of musical instruments: Piano or Keyboard, Guitar (with Tabs and Chords), Piano Accompaniment (also with guitar chords), Main (instruments in C), High (instruments in C), low instruments in C e.g. Bassoon or Cello, instruments in B-flat e.g. Clarinet or Trumpet, Cor Anglais (in F), French Horn (in F), Alto Saxophone (in E-flat) or Viola (alto clef).