public RadForm1()
        {
            InitializeComponent();

            this.radTreeView1.MultiSelect = true;
            this.radTreeView1.AllowDefaultContextMenu = true; 
        } 

        class CustomTreeViewElement : RadTreeViewElement
        { 
            protected override Type ThemeEffectiveType
            {
                get
                {
                    return typeof(RadTreeViewElement);
                }
            }

            protected override bool ProcessMouseDown(MouseEventArgs e)
            {
                if (e.Button == MouseButtons.Right)
                {
                    RadContextMenu menu = this.ContextMenu; 
                    RadTreeNode node = this.GetNodeAt(e.Location);
                    if (node!=null)
                    {
                        node.Selected = true;
                    }
                    if (node != null && node.ContextMenu != null)
                    { 
                        menu = node.ContextMenu;
                    } 
                    if (menu == null && this.AllowDefaultContextMenu)
                    {
                        menu = this.InitializeDefaultContextMenu(node);
                    } 
                    if (menu != null)
                    { 
                        RadControl parentControl = (this.ElementTree.Control as RadControl);

                        if (parentControl != null)
                        {
                            menu.ThemeName = parentControl.ThemeName;
                            menu.DropDown.RightToLeft = parentControl.RightToLeft;
                        }

                        TreeViewContextMenuOpeningEventArgs args = new TreeViewContextMenuOpeningEventArgs(node, menu, this);
                        OnContextMenuOpening(args);

                        if (!args.Cancel)
                        {
                            menu.Show(this.ElementTree.Control, e.Location);
                            return true;
                        };
                    }
                }
                return base.ProcessMouseDown(e);
            } 
        }

        class CustomTreeView : RadTreeView
        {  
            protected override RadTreeViewElement CreateTreeViewElement()
            {
                return new CustomTreeViewElement();
            }
           
            public override string ThemeClassName
            {
                get
                {
                    return typeof(RadTreeView).FullName;
                }
            }

            protected override void WndProc(ref Message m)
            {
                switch (m.Msg)
                {
                    case 0x7b:
                         
                        return;
                }

                base.WndProc(ref m);
            }
        }