Or, if you have some skill with a router, making a template and using a smaller bit is also a possibility.
Magnetic Displays website, and decided it was worthwhile buying these rather than cutting out my own from some magnetic paper. It was a simple matter of peeling of the backing and sticking them in the holes, though I decided to spread a bit of contact adhesive in each hole before doing this to improve the chances of them not coming out in the future.
I can even tilt the base and the trees stay put.
All I need to do now is finish the bases to match my other terrain. I have a different method to show you that is more modular in its approach and is really simple, but that will wait for part three.