If you navigate to the Library settings to add the metadata tree on your library page and you find that the “Metadata navigation settings” item is not there, it’s very simple to fix.
More than likely, it’s because that feature is not activated. Go to Site Actions/Manage Site Features. Activate the ‘Metadata Navigation and Filtering’ feature.
All Things DotNet Discussed – Winforms/ASP.Net/SharePoint/WPF