If you don't want to use up a lot of sprites, you will probably paste sprites to the canvas/paster plugin or draw paths with those (not sure about the paster plugin, has been too long since I've used it).
As to the tree itself, think about:
- branching of one line into 2 or more at a splitting angle.
- a max. amount of branching allowed.
- number of branches per split
- Line lengths (stem is longest, little branches the shortes)
- will it get thinner each branch or continually? continually will be more coding work
- add randomness (lengths, angles, thickness, the possibility for a branch to end before the branch amount maximum)
- leaf "branches" after x-th branch level?
Well, I guess it depends on how complex you want to go into this matter and what effect you want to achieve exactly with this.