Vaadin 8 Tree rendering problem


I’m migrating from Vaadin 7 to Vaadin 8 (I’m not using vaadin-compatability kit).
I tried a sample code for tree (based on demo/sampler source code).
The tree renders without any connecting lines between parent and child nodes (see attached image) and also its not allowing me to select a parent/child node.

Do I need to add any styles to render this?
To migrate from Vaadin 7 to 8, I updated my POM.xml to use vaadin 8.1.7 libraries, downloaded 8.1.7 widgetset and using them.

My source code is below:
Tree tree = new Tree<>(“Hardware Inventory”);

    TreeData<String> data = new TreeData<>();
    data.addItems(null, "Desktops", "Laptops")
        .addItems("Desktops", "Dell GX240", "Dell GX260", "Dell GX280")
        .addItems("Laptops", "IBM T40", "IBM T43", "IBM T60");

    tree.setDataProvider(new TreeDataProvider<>(data));
    tree.expand("Desktops", "Laptops");
    tree.setItemIconGenerator(item -> {
        if (item.equals("Desktops")) {
            return VaadinIcons.DESKTOP;
        } else if (item.equals("Laptops")) {
            return VaadinIcons.LAPTOP;
        return null;
    tree.setStyleGenerator(item -> {
        if (!tree.getDataProvider().hasChildren(item))
            return "leaf";
        return null;



I realised that I have not updated the valo theme. I downloaded 8.1.7 Valo theme from maven repository and now it looks perfect!

Thank you,