I've seen a few people create some trees in 3D which all had the same problem. The easy way to create a tree would be just to take a box, and start doing some extrutions on the top face, and then extrude out some branches. The problem with what I usually see is that they have the main trunk going all the way to the top. That would be good only for an evergreen tree. For a normal tree however, I've put together this small tutorial.
First I will start off with a simple box and convert it to an editable mesh. If you have 3DS Max4 then go with the editable poly since they tend to make a better mesh in the end.
In the polygon sub-object mode select the top polygon and lets start extruding. The trick is to have a shorter trunk. It doesn't go all the way to the top. I usually like to divide my trunk in two and then go from there. The first division of the trunk can be any amount you want.
Remember that its a 3D tree so when extruding faces, don't work in one viewport. Give your tree some depth.
When you have extruded the faces you want to create the shape of your main branches, add a meshsmooth to see what your final tree will look like.
As you can see the bottom of the trunk looks kind of silly. Lets work on the roots a bit. First I select the bottom face of my tree and extrude down twice to create this look. That will stop the bottom from being rounded out like it was before.
Now I take the side faces of our original box and extrude those out to make the roots. its always good to have your landscape turned on so you can see how the roots will look resting on the surface. In this case im just using a box to be my landscape.
Just do some extrutions on each side and your roots are finished.
Time for the leaves.
I start by cloning the tree and hiding one copy of it. The new copy i will delete the polygons making up the lower part of the tree leaving me with the branches. This is done because the leaves will be created using a PArray which will be applied to the branches.
Hide the branches now. The next thing to work on will be to create leaves. You can model them however you want, I just draw a spline and extrude it. I create two leaves shaped slightly different just for a little variation. Normally i would make 3 shapes of leaves, but 2 will do. Then starting with a box i create a brance the leaves will be put on.
I create two different types of branches that the leaves will be on. These branches are small. its better to create longer branches so that your leaves will be further away from your tree trunk than mine turn out to be in this tutorial. Group the leaves and the branch together. And for each branch that you create, create a small box that will be places as the base of that branch and then link your grouped branch to that box. This is because when you use instanced geometry on a group in a particle system, the pivot point is in the middle of the group. we want out pivot at the base.
Create as many PArrays as you have branches. In my case its two. Select tree_copy that you made as your particle emitter and under particle type choose instanced geometry. In the instanced geometry section select the box as the geometry and turn on "use subtree also". For particle rotation i use "user defined" with the settings of 1,1,1 var 0.
particle type rollout look for get material from, and choose "instanced geometry" as your source of material. As for putting a texture to your tree, thats a whole new tutorial in itself. Have fun...