Just brute modeling or looking for scripts to help? Brute modeling: Polyboost/graphite modeling tools > Branch tool Or, Sketchxtrude http://www.scriptspot.com/3ds-max/scripts/sketchxtrude-0-95-beta Scripts and separate apps: Or, TreeMaker script http://www.scriptspot.com/3ds-max/scripts/tree-maker Or, Branchy…
Depending on how close you plan to allow the player or viewer to get, You could simply try some staggered planes with tree photo's/alphas, similar to how Arch Viz guys do background foliage. Obviously you'd need to play with the size/angles of each but it would be a whole lot quicker than modelling anything. Alternatively,…