Don’t use too many fasteners. This gives the tree room to move and grow. Even for smaller, lighter tree houses where the load is spread over three or four attachment points, consider using or lag bolts.
I am insanely JEALOUS! Shared from Avantgardens - Green Roofs Everywhere. Green Roof Shed at Chasewater, Innovation Centre, Brownhills, Staffordshire UK. Photo: Garden Shed by Thislefield Plants & Design