The New York Times writes on the growing demand for treehouses:

Within a few years, elaborate treehouses, many costing upwards of $100,000, were becoming almost faddish.

“It’s accepted now that adults can have treehouses,” said Mr. Nelson, who published four of those books. A partner at TreeHouse Workshop, a building company in Seattle, Mr. Nelson has made up a mantra for some of his clients: “Of course we can have treehouses; we’re baby boomers, and we can have whatever we want, and we can have it now, and we have a lot of money.”