A Unity ID allows you to buy and/or subscribe to Unity products and services, shop in the Asset Store and participate in the Unity community.
Separate names with a comma.
This is the correct answer. Select the terrain -> Select a tree -> click 'Mass place trees' -> Uncheck 'keep existing trees' and set the number...
Did you find a solution to this? I've been having exactly the same problem for a very long time across different versions of unity.