[phyrrus9]

Why should you read the tree from right to left? Is that just protocol, because it seemed simpler to read it as normal from left to right. Also, what exactly does factor refer to in the larger tree? Of course I know what a factor is in mathematics but I'm not sure if this is the same thing.

That's my bad, you're correct it should be left to right.

A factor, in the sense of this project is a parenthesized expression, a number, or a variable.
It looks like in the large tree they like to use (E) form more than anything.