Sort a list of tuples depending on two elements

I have a list of tuples, like so:

[
    ('a', 4, 2), ('a', 4, 3), ('a', 7, 2), ('a', 7, 3),
    ('b', 4, 2), ('b', 4, 3), ('b', 7, 2), ('b', 7, 3)
]

I know that, for example to sort them by the second element, I can use:

sorted(unsorted, key = lambda element : element[1])

But how can I sort the list depending on multiple keys?

The expected result should be like:

[
    ('a', 4, 2), ('b', 4, 2), ('a', 4, 3), ('b', 4, 3),
    ('a', 7, 2), ('b', 7, 2), ('a', 7, 3), ('b', 7, 3)
]