Vertical

• something a little longer
• Item 2
  • Item 2-1
  • Item 2-2
  • Item 2-3
    • Item 2-3-1
    • Item 2-3-2
  • Item 2-4
• Item 3
  • Item 3-1
  • Item 3-2
  • Item 3-3
    • Item 3-3-1
    • Item 3-3-2
  • Item 3-4
• Item 4
  • Item 4-1
  • Item 4-2
  • Item 4-3
    • Item 4-3-1
    • Item 4-3-2
  • Item 4-4
  • Item 4-5
    • Item 4-5-1
    • Item 4-5-2
    • Item 4-5-3
      • Item 4-5-3-1
    • Item 4-5-4
  • Item 4-6
    • Item 4-6-1
    • Item 4-6-2

Remaining requirements:

1. Add scrolling or repositioning to ensure display within window boundaries
2. Fix degradation in IE on Mac