I made the giant pompoms the same way you would using a fork only instead of a fork I used a spatula and I wrapped the yarn 250 times around the spatula for each pompom. I used one Super Saver Jumbo Yarn bundle in white for all the pompoms. That's the jumbo one, not the regular one. It's 744 yards worth of yarn.
Turned out to be just the right size for our little tree!