Here is the full list of all 33 Styx: Master of Shadows achievements. It takes around 25-30 hours to unlock all of the achievements on Windows.
You looked at the World Tree a bit too long...
Finished mission 7
Kill more than 40 guards with throwing knives
Gather all the treasures
Finished mission 6
Kill an enemy who was bound by a clone
Finished mission 5
Pick pocket 15 guards
Finished mission 4
Drink 20 vials of amber
Finished mission 3
Kill an enemy with an aerial kill
Let 15 clones die
Give an orc one of your clones to eat
Kill an enemy by poisoning the food
Create 30 clones
Eliminate a guard with a booby trapped clone
Finished mission 2
Kill two or more enemies by making a chandelier drop on them
Finished mission 1
Kill 20 enemies in duel
Eliminate 200 enemies
Unlock 20 doors
Kill an enemy with a covered kill
Finish the introduction
Kill 50 enemies without making noise
Extinguish 30 torches
Manage to disable three guards, or more, inside a clone's smoke bomb
Unlock all skills
Kill a torturer in a duel
No body found during a mission
Do not use any item during a mission
Unlock the Insignia of the Shadow for each mission