To make a Christmas tree on the wall, you'll need some supplies such as a roll of green paper, a ruler, a pencil, scissors, and some tape. First, measure the height and width of the area you want to cover with the tree. Then, cut out a triangle shape from the paper that fits within these measurements. Next, cut the triangle in half lengthwise to create two separate triangles. These will be your tree's branches. Finally, use the tape to attach the triangles to the wall, overlapping them slightly to create the shape of a tree.