Little mystery

I walk by this door almost every day and today was the first time I noticed something written on it. "In the tree!!" it says.

Looking around the door, which leads off a wide pedestrian lane, there are no trees. The door itself leads (I think) to the bottom of a garden. The wall is about 12 feet high so it's difficult to see if there is a tree that side but, if there is, it's not very tall.

Opposite the door, on the other side of the lane, is another brick wall which runs along someone else's garden. There is a fig tree set quite a distance from the wall but it is very inaccessible.

A little way up the lane is the park where there are lots of trees. I suppose it could mean the tree at the junction of the paths just into the park. In the opposite direction is a road and there are no trees.

And so...a mystery. Or a missed tree. It has me baffled. Also the urgency implied by the two exclamation marks has me even more intrigued. Is this what gloomy days are for, I ask myself. I asked the door but all it said was "In the tree!!"