This is a nice drawing and you actually have a pretty good composition, with breaks in the trees in the right places. They do kinda have branches in real life though, and vary in shape and size alot more than this. You might want to start by breaking up the trunk towards the top and have branches going into clumps of greenery, and vary them a little more in shape. If you put some tall grass or bushes right in the foreground it will give the drawing some depth, too and help it to lay down.
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