I started Umbraco two weeks ago and I try to use sections and trees. After a lot of research I finally made it work but I need some help. Here is my classes:

[Application("tourOp", "tourOp", "Bus.png", 15)]
public class tourOpApplication : IApplication { }
[PluginController("tourOp")]
[Umbraco.Web.Trees.Tree("tourOp", "tourOp_RoomTypes", "Room Types", iconClosed: "Bus.png")]
public class tourOp_RoomTypesController : TreeController
{
    protected override Umbraco.Web.Models.Trees.MenuItemCollection GetMenuForNode(string id, System.Net.Http.Formatting.FormDataCollection queryStrings)
    {
        var menu = new MenuItemCollection();
        menu.DefaultMenuAlias = ActionNew.Instance.Alias;
        if (id.Equals("-1"))
        {
            menu.Items.Add<ActionNew>("Create");
            menu.Items.Add<ActionRefresh>("Refresh");
        }
        else
        {
            menu.Items.Add<ActionDelete>("Delete");
        }
        return menu;
    }
    protected override Umbraco.Web.Models.Trees.TreeNodeCollection GetTreeNodes(string id, System.Net.Http.Formatting.FormDataCollection queryStrings)
    {
        var nodes = new TreeNodeCollection();
        if (id.Equals("-1"))
        {
            var db = ApplicationContext.Current.DatabaseContext.Database;
            foreach (RoomTypeViewModel item in db.Query<RoomTypeViewModel>("SELECT * FROM RoomTypes"))
            {
                nodes.Add(this.CreateTreeNode(item.RoomTypeID.ToString(), id, queryStrings, item.RoomTypeCode + " (" + item.RoomTypeName + ")", "Hotel.png", true));
            }
        }
        return nodes;
    }
}
public class RoomTypeViewModel
{
    public int RoomTypeID { get; set; }
    public string RoomTypeCode { get; set; }
    public string RoomTypeName { get; set; }
}