Starting at the outer edge, simple roll the flower up until you reach the base (or center) of the circle.
I then used a dab of hot glue to adhere the flower to the base. Pretty easy stuff...just takes a long time to make this many flowers.
I also used differing sizes so they would start large at the bottom and get smaller towards the top. After it was all done I zapped the tree with my heat gun to melt away all the hot glue "webs" and then lightly sprayed it with my homemade glimmery mist. (In a mini-mister put water and a few little scoops of Perfect Pearls. I used "Heirloom Gold").