How to use mongo group by in group by?

I have data

[
{name:  'Theara', class: 'A', amount: 10},
{name:  'Theara', class: 'B', amount: 10},
{name:  'Theara', class: 'B', amount: 10},
{name:  'Theara', class: 'B', amount: 10},
{name:  'Theara', class: 'C', amount: 10},

{name:  'Theara2', class: 'A', amount: 10},
{name:  'Theara2', class: 'A', amount: 10},
{name:  'Theara2', class: 'B', amount: 10},
]

The result expected: Group by name, and then by class

[
{name: 'Theara', A: 10, B:30, C:10, total: 50},
{name: 'Theara2', A: 20, B:10, total: 30},
]