Hello there @moldex3d, I hope you're well today!
If you are using the premium plugin then your question should be asked in the WPMU-DEV forums, as on wordpress.org support is provided for the lite plugin. Support on the premium forums is a lot more efficient for premium plugins and is the recommended method.
Now, on to your question:
I want to know how I can active the function (tree structure)show as the image 2 of 8 of screenshots on this page http://premium.wpmudev.org/project/wordpress-wiki/
Do you mean the "sub-wikis" section?