import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.TreeItem;
import javafx.scene.control.TreeView;
import javafx.scene.layout.VBox;

public class App extends Application {
    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) throws Exception {
        TreeView<String> tree;
        TreeItem<String> rootNode, progNode, databaseNode;

        rootNode = new TreeItem<>("Tanulnivaló");

        progNode = createNode("Programozás", rootNode);
        createNode("Java", progNode);
        createNode("Charp", progNode);

        databaseNode = createNode("Adatbázis", rootNode);
        createNode("MySQL", databaseNode);
        createNode("Mariadb", databaseNode);

        tree = new TreeView<>(rootNode);

        Button button = new Button("Vált");
        button.setOnAction(e -> {
            if (tree.isShowRoot())
                tree.setShowRoot(false);
            else
                tree.setShowRoot(true);
        });

        VBox vbox = new VBox(10);
        vbox.setPadding(new Insets(10, 10, 10, 10));
        vbox.getChildren().addAll(tree, button);

        Scene scene = new Scene(vbox, 300, 250);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    public TreeItem<String> createNode(String title, TreeItem<String> parent) {
        TreeItem<String> node = new TreeItem<>(title);
        parent.getChildren().add(node);
        return node;
    }

}