Using ObjectListView/TreeListView you should never use the underlying ListView itself or the ListViewItem objects. Read this
Using the TreeListView in comparison to the ObjectListView is a bit cumbersome.
Example (ignoring the double-click requirement):
private void tvView_SelectedIndexChanged(object sender, EventArgs e) {
// cast your TreeView to ObjectListView to access the selected Object
ObjectListView olv = sender as ObjectListView;
// get the selected child (you may want to check the type and if it really was a child that was selected here)
MyChildModelObject child = olv.SelectedObject as MyChildModelObject;
MyParentModelObject parent = _tvView.GetParent(child);
// ...
}
Since you did not mention the models, I assumed that you have two different model objects in your tree hierarchy (MyChildModelObject and MyParentModelObject).