Or if you're perhaps just referring to an "umbrealla organization" meaning: a media and services company focused on high school PTOs (as PTO Today is focused mainly on K-8), then no, there really isn't one.
Most of our content can be adjusted/applied for high schools, but there's no equivalent service provider for high schools.
Not sure what you mean by umbrella organization. Most PTOs-- elem, MS, or HS are really independent unto themselves, and not part of any higher level organization. If you're looking for advice about highschool PTOs in general, post right here. Surely someone lurking on this site can share their experience and advice.