Creative Twilight has a nice tutorial on making trees from twist ties and joint compound.
Making Snowy Pine Forest Bases
For Osprey Games’popular Frostgrave rules, here’s a tutorial on making snowy pine forest bases.
Modeling Birch Trees
Here’s a tutorial on modeling birch trees. Like palm trees, these are sadly very much underrepresented among cheap plastic model railroad trees.
Making Forest Bases
I like this technique for making bases for your washer-mounted trees. As it is now, I just put the washer mounted trees on a bit of irregularly cut felt.