I downloaded Sapling Tree Gen 2.78 and I can't find any help.
What do the 4 lines of Custom Shape mean?
Blender Stack Exchange is a question and answer site for people who use Blender to create 3D graphics, animations, or games. It only takes a minute to sign up.Sign up to join this community
If you change shape to custom shape, these values will be active.
When you point your mouse on it it says these are the values for Base, Middle, Middle position and Top respectively. You can change those, using your mouse and drag these fields to the left or right or enter number between 0.01 and 1