I am posting this for the simple fact that the speed tree that comes in unreal is more like a slim down basic speed tree version , with limited customization. So I will unveil other programs that will give you more freedom in tree generation . All free and cheap one's , hope this help you guy's to further your level creativity .
1. Arbaro: a free tree generator that gives you a lot of customization in parameters , for the whole tree . http://arbaro.sourceforge.net/
2. tree gen: free , not as good , but faster to use. http://www.treegenerator.com/
3. tree[d]: free , I think this is actually the best tree generator out of the free one's , I love this thing . The only problem is , it is in b3d format and direct x mesh only , but there is an importer for 3d max . tree[d] http://www.frecle.net/index.php?show=treed.about , b3d importer for max http://www.frecle.net/download/3dsmax-b3d-import.zip
4. ngplant : free , this is my second favorite free one . It has alot of customizations , plus texture option's , and it is fairly easy to use . http://ngplant.sourceforge.net/
5. ivy generator: this is a free ivy generator , it is good . http://graphics.uni-konstanz.de/~luft/ivy_generator/
6. tree gen 2: this is not free but it has a good price , this is the second version of the free one that I posted above , and they also share the same link .
7. trees designer: this is not free but a lot cheaper than other tree generators , it is very versatile , and has a unique different way of creating trees than other tree generators , by formation branches around shaped polygon's (orientation polygon reference) , simply draw the shape and plugin will fit a tree into it. As simple as that. grow secondary branches (twigs) that do not have to conform to the shape giving denser and more natural looking trees. the trees look realistic . http://www.polas.net/trees/index.php