TTree and custom classes

Okay, I will try that.
I see a lot of errors that look like this: CoreasEvent.h:9: error: âDouble_tâ does not name a type
What does it mean when it says does not name a type? For reference, that specific error points to this line: Double_t energy; in the class declaration. It also gives similar errors to the other lines in the class declaration.
Would this method require me to add include lines for classes from the root library?