Forrest editor problem

Hello. How can I add trees to the map? I tried Paint tool in Forest editor but it doesn't do anything and unlike terrain editor the paint circle color is grey not pink. Is it impossible in tech demo? This may be silly question but it's just my beginning with map editor. Thx

 

I think not in tech demo as like you can't add more cars.

 

Yes, it got cut from the demo. The demo is just that, a demo. Meant to give a taste, not to provide the whole game via modding.