GridData layoutData = new GridData(GridData.FILL_BOTH);
Tree tree = new Tree(container, SWT.SINGLE);
tree.setLayoutData(layoutData);
categoryTree = new TreeViewer(tree);
categoryTree.setContentProvider(new SnipExCategoriesContentProvider());
categoryTree.setLabelProvider(new SnipTreeViewLabelProvider());
categoryTree.setInput("root");
categoryTree.addSelectionChangedListener(new ISelectionChangedListener(){
public void selectionChanged(SelectionChangedEvent event) {
isPageValid();