Returns the selected nodes in a ObjectCollection.
The returned object collection is Keyed by a TreeViewNode object which means you can pass a TreeViewNode object to the Exists function of the ObjectCollection to query if a specific node is selected.
You can also iterate though the collection by a index to get all the selected nodes.
Warning
Do not use the ObjectCollection returned by this function for anything else than to read from it. Inserting or deleting from the ObjectCollection can and will cause unexpected results in the TreeView.