Time for action – my first tree

Let's start coding right away! Follow these steps to create your first tree:

1. Create a new Vaadin project named my-first-tree using your IDE.

2. Implement your UI class like this one:

   public class MyFirstTreeUI extends UI {
   
     protected void init(VaadinRequest request) {
       final VerticalLayout layout = new VerticalLayout();
       layout.setMargin(true);
       setContent(layout);
       
       Tree familyTree = new Tree();
       
       familyTree.addItem("Families");
       familyTree.addItem("The Jackson");
       familyTree.addItem("The Simpsons");
       familyTree.addItem("The Rothschilds");
       familyTree.addItem("The Hapsburgs");
       familyTree.addItem("The Addams");
       
       familyTree.setParent("The Jackson", "Families");
       familyTree.setParent("The Simpsons", "Families");
       familyTree.setParent("The Rothschilds", "Families");
       familyTree.setParent("The Hapsburgs", "Families");
       familyTree.setParent("The Addams", "Families");
       
       familyTree.setChildrenAllowed(...