I know you're looking for a quick solution...but if you expend even a tiny bit of effort, there is a much easier/cheaper way.
Step 1) Buy some Woodland Scenics armatures: (these come 15-30 in a pack depending on how tall you want them - they can be 3-5" or 5-7" etc. --- see the item when you order)
Step 2) Clip them off the sprue, slap the little base on with some glue and bend the branches around to where you want them (it's a flexible plastic material)
Step 3) Slap on any kind of base you have available, dust it all brown or grey, or whatever you choose. Dry brush the tree armatures if you're in the hobbying mood.
Step 4) Flock the base as needed.
Step 5): DO NOT do the glue/flock method for the trees. Simply buy some woodland scenics (or similar) Lichen in whatever colour combo you want, they even make it blue, beige, red (autumnal), etc.
STEP 6) No glue, just drape the lichen on the trees as you see fit. This means you can remove it later and change it for seasonal changes (or yank it all off and use it in the dead of winter)
Stupid easy, and stupid cheap.
Example use on a
40K table: