A Christmas tree was typically any conifer tree that was decorated with lights and ornaments during the Christmas season. The figure of speech "lit up" or "bypassed like a Christmas tree" was used to describe well lit objects.
In 2372, the crew of USS Voyager found themselves tethered to some kind of large plant, later revealed to be a Christmas tree, after the Q who was later referred to as Quinn reduced the ship to the size of a Christmas ornament, as he attempted to escape from Q. (VOY: "Death Wish")
Soon after, a USS Voyager Christmas tree ornament was produced by Hallmark. The television advertisement promoting it featured a clipshow of the primary characters from VOY Season 1 and VOY Season 2, arranged in a manner to suggest that they were actually promoting the ornament.