The decorations for this tree can come entirely from your landscape. No lights required!
Let some of the flowers in your garden go to seed—after the flowers have bloomed, let what's left continue to ripen. Take the remaining seed pods and glue them onto Styrofoam balls to make large ornaments.
Then, buy a few hundred rosebuds from your local florist. Using a strong needle and thread, string the rosebuds together to make a rose garland. You can do the same thing with small pinecones or acorns, but you may need to use a drill press to make the holes.
The rosebuds will add a beautiful a pop of color to your tree, while acorns and pinecones will give it that classic wintery feel.