viewer.setContentProvider(new ApplyTreeContentProvider());
viewer.setLabelProvider(new ApplyTreeLabelProvider(this));
document.addChangeListener(this);
ExplainTree tree = new ExplainTree(document.getCAS());
viewer.setAutoExpandLevel(2);
viewer.setInput(tree.getRoot());
viewer.addDoubleClickListener(this);
getSite().setSelectionProvider(viewer);
getSite().getPage().addSelectionListener(this);
editor.addCasEditorInputListener(this);
viewer.refresh();