An anonymous neighbor, unhappy with the presence of a treehouse next door, began the process of its removal with a complaint to Minneapolis zoning officials and now the unregulated structure has to go, according to this story in the Star-Tribune. An earlier story contained more details.
As usual in these cases, the offended party, the complainer, the imposed-upon individual, remains anonymous.
The city is probably correct in demanding the destruction of this hold-over from another era. As it's not as regulated as even a playhouse there's always the possibility that some unscrupulously clever social misfit or an organization along the same lines could build a tree manufacturing facility unhampered by city codes and zoning restrictions. Or arboreal housing units that could be inhabited by undocumented aliens. In fact, if treehouse owners allowed Honduran children to move in they could probably get city funding for carpets and electricity.