Hi Badger,
Each "Segment" added to the tree allows you to control it's length and radius. Radius can controlled via specific values or can be inherited as a percentage of it's parent in the graph. You can edit segment profiles for adding custom shapes (e.g. knots, tapering, etc.) to the segment or you can drive displacement with a fractal.
When you activate "blades" on a segment for making leaves with actual geometry, their size is fully controllable in the same fashion and is relative to the segment they are a part of. There is a "Start" offset that allow you to start a blade either right at the beginning of the segment or some point inset into it (essentially allowing for a stem). Similarly, there is an "End" offset which allows you to end the blade prior to the end of the segment.
You can control segment/leaf population via a maximum number and an editable curve which provides for some variation in that number. Alternatively, you can attach random number generators to those inputs and give a maximum number (this is also possible for many other parameters, e.g. length and rotation, etc.).
Hope that helps.
~Micheal
