I have been making trees, using plastic armatures and some with sorghum that we grew last year. I used poly fiber glued to the armatures and then added ground foam and leaf flake using diluted matte medium.
After spreading the sorghum heads, I painted with army green camo, then used the ground foam. Not quite a pine, but still a pretty cheap tree.
The last photo shows a tree armature, but with Supertree branches used instead of the poly fiber, because I ran out of the fiber. I will continue using the Supertree branches because it is a lot easier than making the 15 to 20 fiber tufts for each tree.