I haven't done this but have thought along similar lines. The strangler figs of Tropical America have outstanding possibilities of this type.

Here is where genetic manipulation should be going. The theme has worked over in science fiction a number of times. In one a great hollow, tree-like house was developed. It reproduction is completely controlled and it could not spread into the wilds. The tree had rooms, produced drinking water and certain basic foods for the occupants. It had grass "rugs" and living beds.

Nature has already thought of this. There are trees with hollow thorns or stems to house ants. The tree also forms little bits of food for the ants to keep them in residence. In return the ants defend the tree. If a vine tries to grow up on it or a grasshopper begions to eat a leaf, the ants take it personally and attack. So we are half way there. We've just got to get tree big enough so we can replace the ants!