tiki-wiki: How to create a tree view category structure?

I have a nested category structure, and each structure has some articles. How can I create a tree view structure of all categories.

• If there is any plugin or module let me know.
  
• Also if I should code it, please give me a hint (or a link to documentation) to start coding.
  In addition I don't know why my structure, created by structure feature is empty!

Perhaps you are looking for the Categories module. Structures show structure of wiki pages. Not categories.