This viola arrangement of O Christmas Tree is in the key of C. Select the image below for a printable PDF of the melody. The O Christmas Tree string play-along page has more versions of this carol, so you can play it with other string instruments. The band instrument arrangement of this carol is also in the key of concert C, so you can play along with woodwinds and brass. If you are looking for the song in a different key, visit the main page for O Christmas Tree, which has arrangements in seven different keys, in alto, treble, and bass clefs. More Christmas songs for viola.