I want to improve how I draw my trees so I decided to do some exercises and I practiced a little. As usual, I couldn't leave it at trees and trees alone so I decided to draw a stone house just to shake things up a bit. And yes, somehow I managed to forget to add a window (so it's a dungeon/prison) :p :D
You can see how I started with simple shapes (along with one tutorial which I liked a lot) and went from there. I worked on those simple shapes and managed to create pretty looking trees. As I like drawing from my imagination and I've seen a lot of trees in my life it wasn't that difficult.
I start with circle or oval shape and add some smaller circles. Then I draw the jittery lines to make it appear leafy. After that I add some shadow and taaa-daaaah! It's done. :)
This is the upper half of my paper with trees and unfortunately I had time only to do that. There are some other variants which I have to try out and test, along with different looking trees. I'll go for them too in the next couple of days. If you know a good video tutorial, or if you've seen cool images which I could use to learn let me know in the comments.
All sketches, drawings and photos are my own.
Keep doing what you like and have fun!