public RadForm1()
        {
            InitializeComponent();
            for (int i = 0; i < 5; i++)
            {
                RadTreeNode node = new RadTreeNode("Node" + i);
                for (int j = 0; j < 3; j++)
                {
                    RadTreeNode childNode = new RadTreeNode("Child" + i + "." + j);
                    node.Nodes.Add(childNode);
                }
                this.radTreeView1.Nodes.Add(node);
            }

            this.radTreeView1.MultiSelect = true; 
        }
         
        public class CustomTreeView : RadTreeView
        {
            public override string ThemeClassName  
            { 
                get 
                { 
                    return typeof(RadTreeView).FullName;  
                }
            }

            protected override RadTreeViewElement CreateTreeViewElement()
            {
                return new CustomRadTreeViewElement();
            }
        }

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

            protected override bool ProcessMouseDown(MouseEventArgs e)
            {
                bool isShift = Control.ModifierKeys == Keys.Shift;
                if (isShift)
                {
                    if (this.SelectedNode.Parent != null)
                    {
                        this.SelectedNode.Parent.Expand();
                    }
                }
                return base.ProcessMouseDown(e);
            }
        }