I was checking out art made by Hyrotrioskjan on Deviantart and found his Nea project. One art piece features large genetically modified plants that are able to essentially house a community. These large barrel-like plants grow fast and can be hollowed out to make rooms. I was wondering if such a thing was feasible? Especially considering the side of the plants.
Some trees can already be used as shelter, thanks to the size of their trunk, like baobabs.
To host a community you would need a much more large tree, or better a set of trees with their branches forming a cover, like it has already being done here and there
It doesn't therefore seem too far fetched to have something like you describe.
People are already working on it using tree weaving as a base. The biggest problem is the time it takes to grow the house which is on the order of decades under ideal conditions. perhaps with genetic engineering something more practical might be possible.
take a look at the willow palace in Germany or Patrick Dougherty's tree weaving art.
By figuring out how cells assemble themselves
We're only beginning to understand how cells know where to go in order to form a coherent organism. But say a genius botanist and geneticist figures out the secret, he might as well program a plant to grow a complete house that comes ready with all the furniture. The house could even grow continually new floors, eventually become a tree skyscraper... in a million years. You could even add different reactions to chemicals. Say for example you sprinkle the plant with chemical x, the plant responds to the chemical and grows a living room. Use chemical y and it grows a swimming pool on the roof.
I suggest using a strain of bamboo to create fast growing houses. The fastest growing bamboo was recorded to grow 91cm a day. Bamboo grows by inflating its cells with water, which were grown before the shoot came out of the ground. What's interesting is that bamboo are networked by their roots and can 'pump' water into newly growing shoots. This could also be modified into a sewer system. Just remember that bamboo is an invasive grass and that one tree house will quickly become a treehouse city.