Получить следующий элемент в дереве

Наличие дерева ( логический в БД) с элементами в форме

1. Элемент списка A
2. Элемент списка B
   1. Элемент списка C
      1. Элемент списка D
3. Элемент списка E
4. Элемент списка F
   1. List Item G

and so on (nesting depth not limited), I want to get the next node down (or up), starting from an arbitrary node.

Let's say, List Item D is given I want to write a function GetNextNode() that would return List Item E.

My idea would be to do some recursion stuff, but maybe there is a more clever way to handle this?

My question:

How would you solve this?

EDIT 1:

The tree can be accessed with functions like:

• GetParentNode()
• GetChildrenNodes()
• GetNextSiblingNode()
• etc.

So it's similar to e.g. e Windows Forms TreeView.