raised in question at SO (https://stackoverflow.com/q/64769593/203657)

To reproduce, compile and run, note the blue focus marker

- expected: marker on first item (or no showing at all)
- actural: marker on second item

happens if
- !showRoot
- treeItems added one-after-the-other to root children (with root already attached to tree)

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.TreeItem;
import javafx.scene.control.TreeView;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class App extends Application {

    @Override
    public void start(Stage stage) {

        TreeView<String> treeView = new TreeView<>();
        TreeItem<String> root = new TreeItem<>("Root");
        treeView.setRoot(root);
        treeView.setShowRoot(false);
        
        root.getChildren().add(new TreeItem<>("Foo"));
        root.getChildren().add(new TreeItem<>("Bar"));
        root.getChildren().add(new TreeItem<>("Baz"));

        var scene = new Scene(new StackPane(treeView), 640, 480);
        stage.setScene(scene);
        stage.show();
    }

    public static void main(String[] args) {
        launch();
    }
}