Indeed, oaks and birches tend to be this tool's strong suit, but it would be nice to use it for other tree types. Definitely want Firs, Spruces, and cypresses on the list too.
(Also the strand leaf type leaves a bit to desire in terms of design, they don't quite capture the silhouette of weeping willows, perhaps try having it render wide round bits, then have the strand leaf type protrude from those points?)