What is the irony and symbolism of crumpled money under the mattress?

Amir was taken in an fed by people who could not afford to feed him. Thus, they did so at the expense of their own children, who were left with nothing to eat. The irony in his act of leaving money under the mattress was this was reminiscent of the way he'd framed Hassan many years before. It was almost as if this was a way to make-up for what he'd done to his brother.