What is the difference between stackpane and root in JavaFX?

I'm doing pie charts for JavaFX practice The following is the code for developing pie chart If I use group and stackpane, I find no difference in output I have commented on the group section Just hovering between the two

import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.chart.PieChart;
import javafx.scene.chart.PieChart.Data;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;
public class ChartApp1 extends Application {
public static void main(String[] args) {
launch(args);
}
@Override
public void start(Stage primaryStage) {
PieChart pieChart = new PieChart();
//Group p=new Group();

pieChart.setData(getChartData());
primaryStage.setTitle("PieChart");
StackPane root = new StackPane();
root.getChildren().add(pieChart);
//p.getChildren().add(pieChart);
primaryStage.setScene(new Scene(root,400,250));
primaryStage.show();
}
private ObservableList<PieChart.Data> getChartData() {
ObservableList<PieChart.Data> answer = FXCollections.observableArrayList();
answer.addAll(new PieChart.Data("java",17.56),new PieChart.Data("C",17.06),new PieChart.Data("C++",8.25),new PieChart.Data("C#",8.20),new PieChart.Data("ObjectiveC",6.8),new PieChart.Data("PHP",6.0),new PieChart.Data("(Visual)Basic",4.76),new PieChart.Data("Other",31.37));
return answer;
}
}

Solution

According to the official documentation,

Although the official documentation of the group indicates