TreeViewer treeViewer=....

MergedSelectionProvider selectionProvider = new MergedSelectionProvider();

treeViewer.addSelectionChangedListener(new ViewerSelectionForwarder(selectionProvider, treeViewer));

getSite().getPage().addSelectionListener(new PropertySelectionForwarder(selectionProvider, treeViewer));

getSite().setSelectionProvider(selectionProvider);

public class MergedSelectionProvider implements ISelectionProvider {
	Set<ISelectionChangedListener> listeners = new HashSet<ISelectionChangedListener>();
	IStructuredSelection selection = new StructuredSelection();

	@Override
	public void addSelectionChangedListener(ISelectionChangedListener listener) {
		listeners.add(listener);

	}

	@Override
	public void removeSelectionChangedListener(
			ISelectionChangedListener listener) {
		// listeners.remove(listener);
		// Not allowed do remove any listener, otherwise nobody listen to the property view
	}

	@Override
	public ISelection getSelection() {
		return selection;
	}

	@Override
	public void setSelection(ISelection selection) {
		setSelection(this, selection);
	}

	public void setSelection(ISelectionProvider provider, ISelection selection) {
		if (selection != this.selection) {
			this.selection = (IStructuredSelection) selection;

			fireSelectionChanged(new SelectionChangedEvent(provider,
					this.selection));
		}
	}

	private void fireSelectionChanged(final SelectionChangedEvent event) {
		for (final ISelectionChangedListener listener : listeners) {
			SafeRunnable.run(new SafeRunnable() {
				public void run() {
					listener.selectionChanged(event);
				}
			});
		}
	}

}

public class ViewerSelectionForwarder implements ISelectionChangedListener {

	MergedSelectionProvider provider;
	Viewer viewer;

	public ViewerSelectionForwarder(MergedSelectionProvider provider,
			Viewer viewer) {

		this.provider = provider;
		this.viewer = viewer;
	}

	@Override
	public void selectionChanged(SelectionChangedEvent event) {

		provider.setSelection(viewer, event.getSelection());
		
	}
}

public class PropertySelectionForwarder implements ISelectionListener,
		SelectionListener {

	Set<PropertySheet> properties = new HashSet<PropertySheet>();

	Viewer viewer;
	MergedSelectionProvider provider;

	public PropertySelectionForwarder(MergedSelectionProvider provider,
			Viewer viewer) {
		this.viewer = viewer;
		this.provider = provider;
	}

	// Register property view 
	@Override
	public void selectionChanged(IWorkbenchPart part, ISelection selection) {
		if (part instanceof PropertySheet && !properties.contains(part)) {
			PropertySheetPage p = (PropertySheetPage) ((PropertySheet) part)
					.getCurrentPage();
			Tree t = (Tree) p.getControl();
			t.addSelectionListener(this);
			properties.add((PropertySheet) part);

		}
	}

	// selection change in property view
	@Override
	public void widgetDefaultSelected(SelectionEvent e) { // ignore

	}

	@Override
	public void widgetSelected(SelectionEvent e) {

		if (!(e.item instanceof TreeItem)
				|| !(viewer.getSelection() instanceof IStructuredSelection)) {
			fireSelection(new StructuredSelection());
			return;
		}

		IStructuredSelection sel = (IStructuredSelection) viewer.getSelection();
		if (sel.size() != 1
				|| !(sel.getFirstElement() instanceof XMLEditorElement)) {
			fireSelection(new StructuredSelection());
			return;

		}

		TreeItem t = (TreeItem) e.item;

		if (!(t.getData() instanceof PropertySheetEntry)) {
			fireSelection(new StructuredSelection());
			return;

		}

		XMLEditorElement parent = (XMLEditorElement) sel.getFirstElement();
		PropertySheetEntry pse = (PropertySheetEntry) t.getData();
		XMLEditorAttribute attribute = parent.getAttributeByName(pse
				.getDisplayName());
		fireSelection(new StructuredSelection(attribute));

	}

	private void fireSelection(IStructuredSelection selection) {
		provider.setSelection(selection);
	}

}