You'll have to take this one as food for thought. I had a general idea of what I was going to do here, but after I had tried it, it didn't look as good as it did in my imagination! And most people couldn't tell it was a tree until after I told them. My husband said, "Lime green, huh?"
Start by putting the front section into a piggy.
Here is the part that was trial and error that I would change next time. The idea is to bring the shape of the piggies into a corner like at the top of a Christmas tree. I divided the triangle section in half, but decided I didn't like the part showing. It was taking too long to undo and go back, so I just left it and did something different on the second section.
This time instead of parting down the center, I made a diagonal part parallel to one of the twists. Then the parted sections from the center triangle will cross, one over, one under. Secure them to make the second set of corners.
Twist again and secure with the last sections of hair on the sides. Combine everything at the bottom into the last pony (trunk of the tree). I added a yellow clip like a star at the top. If I had a long green ribbon, I could trace the shape by tucking the ribbon into the hairbands, or I could wrap the whole shape like hair taping. This would all take a lot longer, but it would outline the shape better.
I would be interested to see if anyone can take this idea and make it better. Send me a picture if you like.