Here is the full list of all 14 The Treehouse Man achievements.
Get all achievements
Complete a moonlit river without taking damage
Complete a blue river without taking damage
Complete a red river without taking damage
Find all messages in a bottle
Defeat the corrupter of the cosmic river
Defeat the menace of the fertile river
Find all health upgrades
Unlock all companions
Defeat the arsonist of the barren river
Unlock all weapons
Defeat the arachnid manipulator
Complete a green river without taking damage
Defeat the unborn raptor