I'm trying to hide menu items for a certain DocType is in the tree, however the code below doesn't work as Node.NodeType returns "content" or "media"

How can I get the DocTypeAlias?

I'm using 4.5.2

public class EnterprisePermissions : ApplicationBase
    {
        string donotdeletealias = "textpage";
        public EnterprisePermissions()
        {
            umbraco.cms.presentation.Trees.BaseTree.BeforeNodeRender += new umbraco.cms.presentation.Trees.BaseTree.BeforeNodeRenderEventHandler(BaseTree_BeforeNodeRender);
        }


        void BaseTree_BeforeNodeRender(ref umbraco.cms.presentation.Trees.XmlTree sender, ref umbraco.cms.presentation.Trees.XmlTreeNode node, EventArgs e)
        {
            if (node.NodeType == donotdeletealias)
            {
                node.Menu.Actions.Remove(umbraco.BusinessLogic.Actions.ActionDelete.Instance);        
            }

         }
    }

The code above is from here  http://our.umbraco.org/wiki/reference/api-cheatsheet/using-applicationbase-to-register-events/event-examples/remove-context-menu-items 

Cheers

Rich