You can never make us tell, because we don’t know. Once a year, a group of anonymous elves undertake the brave job of dressing “Fred the Tree” — the lonely “Christmas” tree in the middle of the Old Seven Mile Bridge. They use sophisticated climbing gear, solar panels, ladders and Keys “know-how” to get it done. This year, the display includes a menorah, too. Check it out as you sail over, or under, the hump.