Here are some list of plugins that allow you to create Trees for 3ds max.
The plant factory :
The plant factory has been recently released from e-on but the cgartist out there have
a negative opinion over the pricing. Well there are a variety of different licencing
available though and maybe you can check it out. The Plant factory looks very promising
from the features it allows you to generate all sorts of vegetation.
Exlevel GrowFX :
GrowFX has been out there for a quite a long time and with its continuous updates with
the users needs if right now on the top of the plant generator list. You can directly
create plants/trees within 3ds max and endless possibilities.
Onyx tree storm :
This is almost the oldest tree generators out there. Onyx is very useful for low poly
animated trees within 3ds max. Well it can generate high polys too..with limited
options available for tweaking. But yeah it does the work..
This is a free plugin for 3ds max and allows you to generate trees with limited
options..but what the hell..its free..
Avizstudio Atree3d :
This is one of the most popular plugin which enables you to generate trees with quite a
few options..easy to use and easy to edit..its really a nice plugin as its FREE
Well Xfrog is a nice tree generator..but now getting unpopular..rather its ready to use
models are used much more than its tree generating Software.
Laubwek Plants :