loop – How can I order all subcategories alphabetical independent of the parent categories?

These are my hierarchical three level categories:

- Top-Level Cat 1
  - Sub1A
    - Subchild1A1
    - Subchild1A2
  - Sub1B
    - Subchild1B1
    - Subchild1B2
- Top-Level Cat 2
  - Sub2A
    - Subchild2A1
    - Subchild2A2
  - Sub2B
    - Subchild2B1
    - Subchild2B2
...

Is it possible to get all bottom level category names (the subchildren) and sort them alphabetically independent of the parents? I get all subchildren categories, but they are only orderer alphabetical inside their top level category.

For example I get

Bosnia
Sweden
Congo
Southafrica

From the top level categories Europe and Africa.

But I want to get:

Bosnia
Congo
Southafrica
Sweden