OK so, this game is best played in the car (although you could tweak it to suit your mode of transport). You need at least 2 players. Divide yourself into teams- driver's side vs passenger's side. The aim of the game is to see (and count out loud) as many Christmas trees as possible on the way to your destination. IMPORTANT, you can ONLY count the trees that you pass on your side, trees MUST be decorated, the trees can be inside or outside, as long as it is decorated. This game is often harder for the driver as they have to kept their eyes on the road (apparently!!) so the route you take to your destination is entirely up to 'drive'- this may or may not advantage your driver and incur some elements of what may seem like cheating, this is, to be honest, pretty much in line with the tone of the game! GOOD LUCK- let me know your best scores/ routes/ tactics!
WARNING: you can sometimes be drawn into 'the amazingly decorated house, with lights/father Christmas hanging out of a window etc/ trap' assuming it'll be a score, but if it doesn't have a decorated tree it doesn't count !