I create a simple shape, select a group of voxels at random, and shift them over one voxel to the side to create an organic look to the trunk and branches. The back of the tree has one voxel dark layer to add a more dramatic sense of depth.
I take a base color and stack cubes of three square voxels on the branches to create leaves. For whatever reason, three square voxels strikes me at the perfect size.
Using a darker color, I color the voxels facing the opposite direction of the sunlight, manually creating a basic shadow, and giving a sense of more depth. This requires more fine-tuning than you'd think.
In this case, I use a dramatically lighter (and super unrealistic) color to create light reflections on the tops of the leaves. (This also requires a lot more finagling than you'd think, haha.) Before rendering, I flatten the back of model to optimize for the model for the Unity game engine, then I add a green color to the ground for display!
This is the voxel art tree process I've come up with! I hope you enjoyed seeing the process in action. It took me a long time to find a peaceful middle ground between organic shapes that didn't "fight" the true nature of voxel art. I'll certainly be experimenting more in the future, but I find this style very fitting for To the Wolves.
Check out MagicaVoxel if you're interested in a cathartic art creation experience. I think (hope!) a new version is going to be coming out soon with even more wonderful features for voxel nerds like me!