Ah, a christmas tree on the wall? How intriguing. Let's see......first, we'll need some green construction paper, some glue, and a bit of string. We'll cut out a tree shape from the paper and then we'll hang it on the wall using the string. Next, we'll add some lights to the tree. We can use battery-operated lights or even fairy lights. Finally, we'll add some decorations like ornaments and garlands. And voila! A beautiful christmas tree on the wall!