The most important aspect of a treehouse as it relates to the selected tree is that the design is compatible with the structure of the tree and that construction avoids injury to the trunk, branches and bark. The treehouse will also need to be able to sway in the wind and remain stable without causing harm to the tree by rubbing on the branches. Specific considerations are as follows:

1. Before proceeding, the selected tree should be inspected by a qualified arborist for structural integrity. Any defects should be addressed by pruning or other means in accordance with industry best practices.
2. Whenever feasible, a treehouse should be supported only from the ground, but have the appearance of being supported from within the tree. Most of the benefits of a tree house will be realized without causing undue harm to the tree. In addition, the potential “wind sail” effect of adding the weight and mass of a treehouse will be negated if the treehouse is not directly attached to the branches.
3. Support posts should be carefully excavated by hand, avoiding buttress roots and large support roots.
4. The treehouse structure should be designed with future growth of the tree in mind, which requires careful consideration of the existing branch structure.
5. Significant branches should not be removed to accommodate the treehouse structure. Such wounds are subject to decay and are entry ways to agents causing harmful diseases in trees.
6. No wire, string, rope or other constraints should be tied or slung among the tree branches. The branches will become girdled and subject to decay and failure over time.

An excellent website containing detailed information is www.thetreehouseguide.com