1. Unit 1
   1. Subtopic 2
      1. Subtopic 1
2. Unit 2
   1. Subtopic 2
      1. Subtopic 1
3. Unit 3
   1. Subtopic 2
      1. Subtopic 1
4. Unit 4
   1. Subtopic 2
      1. Subtopic 1
      2. Subtopic 2
         1. Subtopic 1
            1. Subtopic 1
            2. Subtopic 1
         2. Subtopic 2
5. Unit 5
   1. Subtopic 1
6. Unit 6
   1. Subtopic 1
7. Unit 7
   1. Subtopic 1
8. Unit 8
   1. Subtopic 1
9. Unit 9
   1. Subtopic 1