Hi Bari,
The Browse button currently only works on the SketchUp side. The same window (layout and all) needs to be used on both sides, but right now the AutoCAD side is blocking the connection of the browse button.

The Browse button (on the SketchUp side) works to allow you to assign any SketchUp model as the representing component for that tree. Ideally, you'd want to assign a custom tree SketchUp model.

We have two great power tips on how to use this to assign custom components to trees, shrubs, or amentiy reference notes.
Power Tip: Assign a Custom Sketchup Component to a Plant
Power Tip: Create an Amenity RefNote with an Assigned SketchUp Component

You can build you own models, or purchase pre-made models and assign them. We have some recommended sources of SketchUp models on this page.

Thanks,
Amanda