if (categoryNode.level == 1) {
// Main category
final PVerticalPanel categoryPanel = new PVerticalPanel();
categoryPanel.setHeight("1px");
categoryPanel.setWidth("100%");
categoryPanel.ensureDebugId("category_" + categoryNode.name);
categoryNode.ui = categoryPanel;
layoutPanel.add(categoryPanel, categoryNode.name, true, headerWidth);
categoriesByNode.put(categoryNode, categoryPanel);