There is an extended version of the demo scene available.  
To install this please follow this steps. 

1. Install the free Speedtree package from the asset store 
https://assetstore.unity.com/packages/3d/vegetation/speedtree/free-speedtrees-package-29170

2. go to the website https://www.awesometech.no/index.php/vegetation-studio-download-extended-demo/
   Download the demo package for Vegetation Studio Pro on this page and install in the project.		

3. Open the scene DownloadedDemo.scene in the folder AwesomeTechnologies/VegetationStudioProDownloadedDemo