You can use one of the following three methods when adding a child C1TreeViewNode in the designer:
Right-click on the node you wish to add a child node and select Add Child | C1TreeViewNode.
Select the node you wish to add a child node and click on the Add Child button's drop-down arrow and select C1TreeViewNode.
Select the node you wish to add a child node and click on the Edit menu and select Add Child | C1TreeViewNode.