I found this-it might help (scroll down to the diagram)
http://www.thathomesite.com/forums/l...3126209.html?5
eta: this pattern has angles that would be the same as an octagon. At the binding instruction it just says the corners worked fine even though they are not 90 degrees.
http://www.modabakeshop.com/2010/06/...r-my-tree.html