Here is my 100% Achievement guide and full walkthrough for Tell Me Why (Chapter 2).
After you clean the house, you will be in the car with Tyler and have to take a phone call.
When you regain control of Alyson, head up the only path to the rock where Tyler is sitting (just a short stroll).
After a long conversation here, you start heading back towards the car but just before you do, Tyler will head off to the left and make an adjustment on a tree..
Achievement unlocks here.
Go to 47:00 if you want to see where this is
Hope this helps!