php - symfony3 save object to mongodb -

i json object front-end application this:

{ key1: 'value1' key2: {   key3: 'value3',   key4: {     key5: 'velue5' } } } 

in form how can tell symfony key2 instance object composed of multiple fields, want this:

    $builder         ->add('key1', type\texttype::class)         ->add('key2', object, [            'key3' => type\texttype::class     ]);