NavigationNodeCollection class

public sealed class NavigationNodeCollection : ClientObjectCollection<NavigationNode>

using System;
using Microsoft.SharePoint.Client;

namespace Microsoft.SDK.SharePointFoundation.Samples
{
    class NavigationNodeCollectionExample
    {
        static void Main()
        {
            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);
        }
    }
}