Determining the depth of a nested HTML list

• Tree 1-1
• Tree 1-2
  • Tree 1-2-1
  • Tree 1-2-2
  • Tree 1-2-3
• Tree 1-3
• Tree 1-4
  • Tree 1-4-1
  • Tree 1-4-2
    • Tree 1-4-2-1
    • Tree 1-4-2-2
      • Tree 1-4-2-2-1
      • Tree 1-4-2-2-2
  • Tree 1-4-3
• Tree 1-5
• Tree 1-6

• Tree 2-1
• Tree 2-2
  • Tree 2-2-1
  • Tree 2-2-2
• Tree 2-3
• Tree 2-4
• Tree 2-5

• Tree 3-1
• Tree 3-2
• Tree 3-3
• Tree 3-4
• Tree 3-5