AST interpreter?

I have an AST (abstract syntax tree) and now i want to test my compiler by giving it 2 or more numbers and expect an output with the result of math operations (like a calculator).

My question is, what is the best way to build the interpreter? The visiting of the AST nodes is recursive, so i don't know how many encapsulated calculations exists until i get to the end of the tree. But since this is done iteration by iteration, how can i make all the operations in the end?

Thank you