FlyTreeView for ASP.NET 1.1 has the only ability to add nodes - add them from well-formed XML (like in NodeSrc example) using the node.AddNodes(...) method.
Anyway it looks like you rather need to postback to immediately update database. So you can add node at server-side. This way is much more simple, since you just need to handle context menu click and postback page in order to add a node and update database.