First of all, you need to divide the hangers into three groups of two each. Take the twist ties and tie up one of the corners together from each group of hangers. Make sure the hooks are in the middle when you tie up the corners. After you have tied the hangers, you should get a tripod with the hooks hanging down in the middle.
Now when you spread out all the six hangers, they should extend outwards like a fan, forming the frame of a tree. The hooks of the hangers should be sticking outwards at the bottom end of the frame. You have to fasten each hook to the wire hanger besides it and this will make a stable frame for your tree.
You better place the wires for lighting on the tree at this point. Dangle down the plug of the lights in the middle of your miniature tree and fasten it to the base of the tree. You can use a twist tie for affixing the plug.
Now start wrapping lights around every wire hanger. You can use a yarn for fastening the strands to the hanger. Make sure to cover up the entire surface of wire hangers.
Begin enfolding the garland around the tree, starting from the top and dangling it downwards to the middle of the tree. Make sure to expose any lighting that hides behind the garland.
You can use any other decorative items available at your home to make your tree topiary look even elegant.