This season 7 week 6 quest requires you to destroy 5 alien trees.

The alien trees will only grow in certain areas of the island. If you bring up the map you will see several purple looking areas. The biggest is The Aftermath and the surrounding area. The Aftermath is at the center of the map where The Spire used to be in the previous season.

Head over to any of these locations and use your pickaxe to destroy any 5 trees. The shrubs and bushes will not count towards this quest.