I found a plug-in for SketchUp that can build components of a tree, shrub and even ground cover in 2D.
It’s RpTreeMaker by RenderPlus.

Plug'in RpTreeMaker
Plug’in RpTreeMaker

You can download this free plug-in on the site after giving some information about you.
You will get an installation kit that takes care of everything. Once installed you access the plug-in through the “RpTreeMaker” little box that appears at SketchUp launching or by “Plugin” menu.

To get an idea I would recommend this video…