如何用JavaFX在树形表视图上显示边框？

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

TreeView<String> treeView = new TreeView<>();
TreeItem<String> root = new TreeItem<>("Root");
treeView.setRoot(root);

TreeItem<String> child1 = new TreeItem<>("Child 1");
TreeItem<String> child2 = new TreeItem<>("Child 2");
root.getChildren().addAll(child1, child2);

BorderPane borderPane = new BorderPane();
borderPane.setCenter(treeView);

Scene scene = new Scene(borderPane, 400, 300);

primaryStage.setScene(scene);
primaryStage.show();

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

public class TreeViewExample extends Application {

    @Override
    public void start(Stage primaryStage) {
        TreeView<String> treeView = new TreeView<>();
        TreeItem<String> root = new TreeItem<>("Root");
        treeView.setRoot(root);

        TreeItem<String> child1 = new TreeItem<>("Child 1");
        TreeItem<String> child2 = new TreeItem<>("Child 2");
        root.getChildren().addAll(child1, child2);

        BorderPane borderPane = new BorderPane();
        borderPane.setCenter(treeView);

        Scene scene = new Scene(borderPane, 400, 300);

        primaryStage.setScene(scene);
        primaryStage.show();
    }

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