Currently the Document Index display a livetable with actions for the containing pages and also a Tree, see currentDocumentIndex.png
Currently Wiki Index displays just a livetable with actions, see currentWikiIndex.png
There is no global Tree in order to scan throughout the wikis.
Still, for example such a tree is available in the Copy/Rename actions, see copyTree.png
1. A solution would be to add a "Tree" tab in Wiki Index
2. Another solution would be display this Tree on xwiki:Main.WebHome. Just like AS display global events, the Tree could also display global structure.
3. Incorporate global tree in breadcrumb menu, see