I got the idea for these cards from an old Paper Crafts Magazine (2006).
I punched strips of green cardstock with my floral lace border punch (Martha Stewart), and glued it to a white piece of cardstock.
Next I traced the pattern of the tree on the back and cut out it out.
Not wanting to waste my paper I did some "upside-down" too.
You can find free tree templates here.
(NOTE: I made mine a bit skinnier than this template.)