empty paper towel roll
brown and black paint
Do the same on the bottom and make roots.
Take each "limb" and crease down the center lengthwise, making sure some curl under, some point up and/or out.
Paint the entire tree dark brown with black highlights.
After it's dry you can re-crease the limbs and spread the roots out so that it will stand on its own.
You can paint the inside orange, cut out eyes and a mouth and drop down a little battery operated light inside for a really spooky effect, too.