php - create array of object with array

I am working on a exam portal project in laravel. I want to create an array of objects. One object must have student name property and in that same object I want to push another subject array for that student. I want output like this...

[
    {
        "student": "Jaime Thomas",
        "subjects": [
            {
                "subject": "Physics",
                "marks_": 0
            },
            {
                "subject": "Chemistry",
                "marks_": 0
            }
        ]
    },
    {
        "student": "Jaime Dey",
        "subjects": [
            {
                "subject": "Physics",
                "marks_": 0
            },
            {
                "subject": "Chemistry",
                "marks_": 0
            }
        ]
    }
]

Here is my code...

$exam_data = tbl_exam_data::join('tbl_subjects', 'tbl_subjects.subject_id', 'exam_data_subject_id')
            ->where('exam_data_exam_id', $exam_id)->get([
                'exam_data_id', 'subject_name', 'subject_id', 'has_negative_marking', 'negative_marks'
            ]);
        $exam_details = tbl_exam::find($exam_id);
        $usersData = User::where('user_id', 2)->where("stud_class", $exam_details->exam_class_id)->where("stud_sub_branch", $exam_details->exam_branch_id)->get(['name', 'id']);
        $studentsArray = [];
        foreach ($usersData as $user) {
            $studentsArray = array(
                "student" => $user->name,
                "subjects" => []
            );
            foreach ($exam_data as  $subject) {
                $att_exams =  tbl_student_attended_exam::where('attended_exams_subject_id', $subject->subject_id)
                    ->where('attended_exams_student_id', $user->id)
                    ->first();
                if ($att_exams) {
                    $marks =  tbl_student_attended_questions::where('student_attended_question_std_exams_attended_id', $att_exams->attended_exams_id)->get();
                    $right = 0;
                    $wrong = 0;
                    $total_marks = $marks->sum('student_attended_question_marks');
                    foreach ($marks as $mark) {
                        if ($mark->student_attended_question_is_correct_answer == 0) {
                            $wrong++;
                        } else {
                            $right++;
                        }
                    }
                    $total_negative_marks = $wrong * $subject->negative_marks;
                    $subjectsArray[] = array(
                        "subject" => $subject->subject_name,
                        "marks_" => $total_marks - $total_negative_marks,
                    );
                } else {
                    $subjectsArray[] = array(
                        "subject" => $subject->subject_name,
                        "marks_" => 0,
                    );
                }
            }
            $studentsArray[]["subjects"] = array($subjectsArray);
        }
        return $studentsArray;