Holding on/sitting on a Christmas tree and being dragged around while it is pulled by a vehicle. This is accomplished by tying one end of a rope to the tip of a Christmas tree and the other end to a tow hitch on the vehicle. The rider sits on the tree and then the driver pulls him/her around along with the Christmas tree, and hence "surfs" across the street/lawn.
Did you hear about the guy who wiped out while Christmas tree surfing? He hit a parked car and is now in the hospital!