Start by making the base of the sculpture. Use a large metal or metallic-colored flower pot as your base. Fill it with aquarium gravel, leaving 2 inches at the top. Pour craft resin over the gravel to keep it in place. While the craft resin is still wet, apply a layer of metallic marbles to the top 2 inches of the pot. Cover these with a layer of clear craft resin, then stick the dowel rod about 3 to 4 inches into the center of the pot. Use more resin to fill in any gaps created by the rod. Allow to set overnight.
Create the branches by wrapping heavy gauge wire around the center rod and extending the piece of wire out as long as you'd like your branch to be. Create several different branches of varying sizes. Use pliers to twist the wire tight, denting the dowel rod so that it doesn't slip or move.
Use a hammer and nail or a drill to create two holes in the bottom of each can that are large enough for your wire to fit through. Begin attaching your cans to the end of your wire branches by threading wire through one hole, around and back out through the bottom hole, then twisting with pliers to secure. The more cans you apply, the fuller your tree will be. The cans will droop and stack on top of each other, so this art piece looks better with many, many cans.
Lay newspaper or drop cloth on the floor around your sculpture and use metallic spray paint to cover any visible wood on the dowel rod. You can also spray paint accent colors on to your cans.
Move the sculpture to the place where you'd like it to be located. Bend your wire branches and move your cans until your sculpture looks exactly how you'd like it.