string siteUrl = "http://MyServer/sites/MySiteCollection";
ClientContext clientContext = new ClientContext(siteUrl);
Web site = clientContext.Web;
// Get the Quick Launch navigation node collection.
NavigationNodeCollection collQuickLaunchNode = site.Navigation.QuickLaunch;
// Set properties for a new navigation node.
NavigationNodeCreationInformation ciNavicationNode = new NavigationNodeCreationInformation();
ciNavicationNode.Title = "New Node";
ciNavicationNode.Url = "http://localhost";
// Create node as the last node in the collection.
ciNavicationNode.AsLastNode = true;
collQuickLaunchNode.Add(ciNavicationNode);
clientContext.Load(collQuickLaunchNode);
clientContext.ExecuteQuery();
Console.WriteLine("Current nodes:\n");
foreach (NavigationNode navNode in collQuickLaunchNode)
Console.WriteLine(navNode.Title);