Display
At the portal level, you can define whether the page list in the SideBar is Compact (display the first-level pages with the option to view child pages) or TreeView (displays all pages with appropriate indentation to indicate parent/child relationships between pages).
NOTE: TreeView applies to the simplified interface only. The classic interface SideBar shows the compact display regardless of the portal display setting.
At the page level, you can specify if the SideBar uses standard behavior or if is either open or closed by default.
Behavior
When you navigate to a top level page with content, the standard behavior is for the new page to start with the SideBar closed. In all other cases, the page starts with the SideBar open.
SideBar Pushpin (Classic Interface Only)
Pinning the SideBar forces it to remain open when any page is selected, until you unpin it or log off.
To pin the SideBar open, click the SideBar pushpin icon. This overrides the SideBar navigation property setting. Click the pushpin icon again to unpin the SideBar.