The best way to make a Christmas tree with lights on the wall is by using string lights. Start by measuring the area you want to cover with the lights and purchase enough string lights to fill the space. Once you have the lights, hang them on the wall in a tree-like shape, with the top of the tree at the top of the wall and the bottom of the tree at the bottom. You can then decorate the tree with ornaments or garlands to make it look even more festive!