
CandyFace
He is taking advantage of the tile feature.
How to: add the first tree to the tileset (the Tiles window to the right), then place copies of that tree in all those tiles on the canvas, so they share the same tile number, in my case to 0, then all changes will affect all the mapped tree clones.
Let me demonstrate:

The trees which are not mapped to the same tile number, won't be affected.
To add a tile from the canvas to the tileset, hold down ctrl + click or cmd + click on mac, on the tile, then it'll appear in the "Tiles" window. Hover over the "Tile placer tool" button to see what other actions are available :)
How to: add the first tree to the tileset (the Tiles window to the right), then place copies of that tree in all those tiles on the canvas, so they share the same tile number, in my case to 0, then all changes will affect all the mapped tree clones.
Let me demonstrate:

The trees which are not mapped to the same tile number, won't be affected.
To add a tile from the canvas to the tileset, hold down ctrl + click or cmd + click on mac, on the tile, then it'll appear in the "Tiles" window. Hover over the "Tile placer tool" button to see what other actions are available :)