SPSecurity.RunWithElevatedPrivileges(delegate ()
            {
                using (SPWeb web = (SPWeb)properties.Feature.Parent)
                {
                    Boolean found = false;
                    SPNavigationNodeCollection nodes = web.Navigation.QuickLaunch;
                    foreach (SPNavigationNode node in nodes)
                    {
                        if (node.Url.ToString() == "_layouts/15/ContractManager/ContractManager.aspx")
                        {
                            found = true;
                        }
                    }

                    SPNavigationNode navNode = new SPNavigationNode("Contract Manager", "_layouts/15/ContractManager/ContractManager.aspx", true);
                    if (found == false)
                    {
                        web.AllowUnsafeUpdates = true;
                        nodes.AddAsLast(navNode);
                        navNode.Update();
                    }
                }
            });