Use of parenthesis in the body of abstraction in lambda expression

In the lambda expression $$(λx. (λy. (x y)) y) z$$, the body of the abstraction is taken as $$(λy. (x y))y$$ and not just $$(λy. (x y))$$. Why isn't $$(λy. (x y))$$ considered as the body and the following $$y$$ as an argument to it instead of $$z$$ being an argument to the body $$(λy. (x y))y$$?