[Haskell-beginners] Help with a data type declaration

How can I interpret the following data type declaration? The book where I am studying (and other sources I have read as well) only show more simple examples. This is what I can say about it: * "Tree" is the name of the new type. * "Branch" and "Leaf" are the type constructors. * What is "a" and "b"? * It seems to me that this type is kind of "recursively" defined but I do not know exactly. data Tree a b = Branch b (Tree a b) (Tree a b) | Leaf a I will very much appreciate your feedback. Regards, JAMB