Speedtree is included in Trainz 2010, but not the Speedtree software that makes the trees, as this part of the program is highly expensive, which was mentioned above.
There are a selection of trees available from speedtree in Trainz 2010, visit the trainz 2010 website and have a look at the new video's that include the new speedtrees along with the screenshots of the various trees available.
These trees are also seasonal activated, which means if it's winter, the trees will have no leaves on them, but the twigs might have snow, if it's Autumn the trees will have brown leaves, the trees also sway as though wind is passing through them, the only sad thing is, I don't think they will have shadow activation, which means the trees will have no shadows attached to them.
Hope this helps
Joe Airtime