The process is simple enough, just drill a hole where you want a tree. You want the drill bit to be a little smaller than the trunk width, if its too big then you will find it fiddly when gluing the tress.
I went for a mixture of two tree and three trees per base. I found that putting the tree closer to the edge of the base so that the limbs overhang looks best. It helps hide the base and allows you to bunch up trees to represent thick or heavy woods.
Since the trees were the same height (all 100 of them) I trimmed a little bit off the stem/trunk of each tree before pushing it into the base. As you can see here the fit is quite snug and probably wouldn't need gluing but I did anyway just make sure, after all these are going to get a bit of handling on the table. Just a small dab of superglue at the base of the trunk will suffice.
My first few completed stands, even now it's starting to look like a little woods.
As you can see, I forgot about the slotta tab slot. A bit of paper will do the trick but it was fiddly getting it in there.
So I stopped drilling and glued over the slot on the remaining bases first.
After all the bases had been drilled and trees glued into place I painted all the bases dark green (from memory GW Salamander Green methinks).
Almost done and looking good, just a bit of flock and they'll look even better. So out comes the flock and my trusty tub of "watery glue sludge".
And then I'm left with this:
Just a few shots of the trees in action. I'm really happy with these, and best of all is that it only took around two hours from start to finish. I'll be getting some more of these for sure, you can never have too many trees on the table.