Where to store data common to all events in a TTree?

quite often I am in a situation where I have a list of events but also some data that is common to all the events.
I would like to save such a structure in a TTree. I guess/hope the answer is easy, but Im not sure what is the best way to do this…

An example would be

Double_t event_data[number_of_events][size];
Doulbe_t some_data_common_to_all_events;

To store the event_data, I would create a branch to hold Double_t[size], but where to put some_data_common_to_all_events ?


The placeholder for such information is TTree::GetUserInfo where you can store TParameter object if you need to store just a single value.