To use mesh to decorate a Christmas tree, start by cutting the mesh into strips of various lengths and widths. Then, wrap the strips around the tree in a criss-cross pattern, using floral wire to secure them in place. You can also add other decorations such as lights, ornaments, and garland to enhance the overall look. Once the mesh is in place, you can further customize the tree by adding a star or angel at the top. Happy decorating!