I recently made one of these origami tree cards, and it was SO much fun!! And, it's not nearly as hard as it looks (yea)! I thought I'd give you some step-by-step instructions so you could make one on your own. For my card, I used paper from the Pear & Partridge paper packet. I like a nice heavyweight patterned paper (but not cardstock) for the tree.
By the way, I HIGHLY recommend a bone folder tool for these projects--we carry a great one in our catalog (Z1204 for $4.95). Your folds will be so much more crisp with this tool. Anyway, begin by folding one of your squares in half diagonally (desired pattern on the outside). Open it up and fold it again diagonally in the opposite direction.
At this point, your paper looks like the roof of a house.
Squeeze in two opposite sides of your roof and fold the roof down into a triangle. Your piece will now be a triangle with two "layers." You may need to use your bone folder or fingers to work it into a nice point on the top.
Set your triangle down and fold one of the layers on the front of your triangle down toward the middle.
Once your squares are folded, glue your SMALLEST piece to the top of your base card/project. Then, tuck the next piece slightly inside of it and glue it down. Continue on with the next bigger piece and then, finally, the largest piece.