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