How to groupBy in nested collection Laravel?

I have this collection by query below and I want to group all elements by curriculum_id like this

public function getByClassroomId($classroomId)
{
    $marks = ClassroomMarkBook::with([
        'classroomSubject' => function ($query) use ($classroomId) {
            $query->where('classroom_id', $classroomId);
        },
        'classroomSubject.subject'
    ])->get();

    $result = [];

    foreach ($marks as $mark) {
        if(!is_null($mark->classroomSubject)){
            $result[$mark->student_id][$mark->classroomSubject->id][] = $mark;
        }
    }

    return $result;
}

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