Using my CheckBoxCell test application, I run into problems where even after expanding a branch the items do not show. This does not appear when using a simple cell factory, e.g.

treeView.setCellFactory(new Callback<TreeView<String>, TreeCell<String>>() {
            @Override public TreeCell<String> call(TreeView<String> tv) {
                return new TreeCell<String>() {
                    @Override
                    public void updateItem(TreeItem<String> item, boolean empty) {
                        super.updateItem(item, empty);
                        setNode(new Label(item == null ? "" : item.getValue()));
                    }
                };
            }
        });