Steps to reproduce:

1. Open a Unity project
2. Download and Import this asset to your project: Free Trees  
3. Open the Undo History via Ctrl + U or Edit > Undo History
4. Add a Terrain to your scene via GameObject > 3D Object > Terrain
5. Select the new Terrain GameObject
6. In the Inspector, under the Terrain component, navigate to the 'Paint Trees' tab
7. Click on Edit Trees > Add Tree
8. Select one of the imported tree assets next to the Tree Prefab option
9. Click Add
10. Observe the Undo History
11. With the tree selected, click Edit Trees > Edit Tree
12. Next to Tree Prefab, select a different tree asset
13. Click Apply
14. Observe the Undo History
15. With the tree selected, click Edit Trees > Remove Tree
16. Observe the Undo History

Actual results: Removing a tree adds to the Undo History as expected, however Adding and Editing a tree do not

Expected results: Adding, Editing, and Removing a tree all add to the Undo History

Reproducible with versions: 6000.0.21f1, 2022.3.48f1, 2021.3.44f1

Not reproducible with versions: - 

Can’t test with versions: 7000.0.0a3 (terrain system no longer available)

Tested on (OS): Ubuntu 24.04, Windows 11

Notes: 

• Depending on the order that you Add/Remove/Undo trees, this issue can have some extra weird behaviour. For example, if you

   1. add a tree to the Trees list
   2. remove that tree 
   3. add that same tree again 
   4. undo the removal of that tree 
   5. redo the removal of that tree 
then the tree will be gone, even though the previous step had the tree still there. This is because of adding trees not being added to the Undo History.