Displaying Site Navigation with Tree View
You can use Tree View to display items from SharePoint Lists, Document Libraries, Discussion Boards, Wikis and Picture Libraries or to display sites in the site collection.
|From the left pane, click the plus sign
Click the site item name to view sub-sites in the right pane.
NOTE: Depending on how it has been configured, your web part may have a Create link above the tree view. Users with the appropriate permission level, will be able to create a new SharePoint site under the selected node.
Clicking the name of the sub-site or the icon takes you to that site.
You can also limit the tree hierarchy to show only sites under the current site by selecting the Only this site and below check box in the Web Part tool pane. See Step 2 in Configuration Options SharePoint Site.