The tree "trunk" is nothing more than a twisted wire, on railroad layouts they are designed to be pressed into polystyrene terrain. But for us wargamers we usually have our trees on a flat base for ease of gaming, preferably removable to make way for troops.
My bases are mdf trays (I got them from warbases, they are actually advertised as pond bases but I thought they were a good size for small copses/scatter terrain). How to get the tree to stand up on them? I toyed with the idea of bulking the trunk up with masking tape and using it to somehow stick to the bases, but it never really seemed a good idea and would also require additional painting. I wanted something a bit quicker and easier.
The idea to use wooden beads came from my wife. They already have a hole so no need for drilling. Just glue them to the base, pop in a tree, job done. There are probably better ones available, more cylindrical rather than round, but these were in the house so they got used.
I applied some ground texture using a mix of diluted pva glue, sand and small stones, and tile grout. This is essentially what I use on my figure bases. I made it quite fluid and poured it onto the bases rather than apply with a brush or stick, then added extra sand to firm it up. When it was partly dry I pushed it up around the beads to hide them better.
With the trees in place the beads are practically invisible, and when they are painted I reckon they will just disappear. I am hoping that I literally will not be able to see the wood(en beads) for the trees! I will report back when they are finished.