Hi Benny,

Thank you for your question.  Tree houses and kids just go together, don't they?  I'm not sure what you mean by sustainable, but since I'm answering from the Horticulture and plant protection perspective, I will take that to mean that it will sustain/protect tree health.  

From the Horticultural perspective, never wound a tree with nails, screws/bolts, or saw notches into the trunk or branches.  Any injury to the bark and tree tissue provides entry to pests and diseases and is not recommended from a tree health perspective. Large cuts into the bark will interrupt the flow of water and nutrients to outer areas of the tree, so can have significant negative impact.   Some tree-friendly options would involve resting the tree house on major branches and nestling it around the tree trunk.  Use strap attachments instead of bolts, or use wooden supports (stilts).

That being said, Trunk Attachment Bolts (TABs) are used in the industry.  Before you go that route, read through some options listed in the references below, and be sure to consult a certified arborist.

References

• Tree-Safe Tree House  https://newswire.caes.uga.edu/story/3645/tree-safe-tree-houses.html
• Tree Injuries, Prevention and Care  https://forestry.usu.edu/trees-cities-towns/tree-care/tree-injuries
• International Society of Arboriculture:  Find an Arborist Tool:  https://www.treesaregood.org/

Sorry that I couldn't find more practical resources.

Best,

Mari