您的代码需要一些修复:

Your code need some fixes:

1. menuItem是父节点，不需要RouteValues.
2. 基本上，父节点需要SystemName

1. menuItem is a parent node, does not required RouteValues.
2. Basically, parent node needs SystemName

进行较大更改后，父节点应如下所示:

After doing upper changes, the parent node should be look like:

var menuItem = new SiteMapNode
{
    Title = "Promo Slider",
    Visible = true,
    SystemName = "Widgets.PromoSlider",
};

好吧，现在进入子节点，您每次都在创建一个新节点.而不是添加到父节点！

Okay, now coming to the child nodes, you're creating new node each time..instead of add to the parent one!

var createUpdate = new SiteMapNode()
var manageSlider = new SiteMapNode()

因此，将其更改为:

menuItem.ChildNodes.Add(new SiteMapNode
{
    SystemName = "Widgets.PromoSlider",
    Title = "New Sliders",
    ControllerName = "PromoSlider",
    ActionName = "CreateUpdatePromoSlider",
    Visible = true,
    RouteValues = new RouteValueDictionary() { { "area", null } }
});

menuItem.ChildNodes.Add(new SiteMapNode
{
    SystemName = "Widgets.PromoSlider",
    Title = "Manage Sliders",
    ControllerName = "PromoSlider",
    ActionName = "ManagePromoSliders",
    Visible = true,
    RouteValues = new RouteValueDictionary() { { "area", null } }
});

最后，将父节点添加到插件"节点:

At the end, add parent node to the Plugins node:

var pluginNode = rootNode.ChildNodes.FirstOrDefault(x => x.SystemName == "Third party plugins");
if (pluginNode != null)
    pluginNode.ChildNodes.Add(menuItem);
else
    rootNode.ChildNodes.Add(menuItem); 

全部完成！运行它，它将根据需要显示.

All done! Run it and it will display as you want.