Root
  Top level 0
  Top level 1
  Top level 2
        Leaf 20
        Leaf 21
        Leaf 22
  Top level 3
        Leaf 30
        Leaf 31
        Leaf 32
  Top level 4
        Leaf 40
        Leaf 41
        Leaf 42

Root
  Top level 2
        Leaf 20
  Top level 3
        Leaf 30
  Top level 4
        Leaf 40

import java.util.ArrayList;
import java.util.List;

import org.eclipse.jface.layout.GridDataFactory;
import org.eclipse.jface.layout.GridLayoutFactory;
import org.eclipse.jface.viewers.ILazyTreeContentProvider;
import org.eclipse.jface.viewers.LabelProvider;
import org.eclipse.jface.viewers.TreeViewer;
import org.eclipse.jface.viewers.Viewer;
import org.eclipse.swt.SWT;
import org.eclipse.swt.events.SelectionAdapter;
import org.eclipse.swt.events.SelectionEvent;
import org.eclipse.swt.widgets.Button;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;

public class TreeSnippet {

	public static void main(String[] args) {
		Display display = new Display();
		Shell shell = new Shell(display);

		GridLayoutFactory.fillDefaults().applyTo(shell);
		Button b1 = new Button(shell, SWT.PUSH);
		GridDataFactory.fillDefaults().applyTo(b1);
		b1.setText("Update");
		final TreeViewer treeViewer = new TreeViewer(shell, SWT.VIRTUAL | SWT.BORDER | SWT.MULTI);
		GridDataFactory.fillDefaults().grab(true, true).applyTo(treeViewer.getControl());

		treeViewer.setContentProvider(new MyContentProvider());
		treeViewer.setLabelProvider(new LabelProvider());

		b1.addSelectionListener(new SelectionAdapter() {
			@Override
			public void widgetSelected(SelectionEvent e) {
				updateModel((TreeNode) treeViewer.getInput());
				treeViewer.refresh();
			}
		});

		treeViewer.setInput(getInitialModel());

		shell.open();
		while (!shell.isDisposed()) {
			if (!display.readAndDispatch())
				display.sleep();
		}
		display.dispose();
	}

	/*
	 * defines initial version of the model
	 */
	private static TreeNode getInitialModel() {
		TreeNode result = new TreeNode(null, "Root");
		new TreeNode(result, "Top level " + 0);
		new TreeNode(result, "Top level " + 1);
		for (int i = 2; i < 5; i++) {
			TreeNode tl = new TreeNode(result, "Top level " + i);
			for (int j = 0; j < 3; j++) {
				new TreeNode(tl, "Leaf " + i + "" + j);
			}
		}
		return result;
	}

	/*
	 * changes the model
	 */
	private static void updateModel(TreeNode model) {
		for (int j = 2; j < 5; j++) {
			for (int i = 2; i > 0; i--) {
				model.children.get(j).children.remove(i);
			}
		}
		model.children.remove(0);
		model.children.remove(0);
	}

	private static final class MyContentProvider implements ILazyTreeContentProvider {

		private TreeViewer treeViewer;

		@Override
		public void dispose() {
		}

		@Override
		public void inputChanged(Viewer viewer, Object oldInput, Object newInput) {
			treeViewer = (TreeViewer) viewer;
			treeViewer.refresh();
		}

		@Override
		public void updateElement(Object parent, int index) {
			TreeNode node = (TreeNode) parent;
			if (index < node.children.size()) {
				TreeNode element = node.children.get(index);
				treeViewer.replace(parent, index, element);
				updateChildCount(element, -1);
			}
		}

		@Override
		public void updateChildCount(Object element, int currentChildCount) {
			TreeNode node = (TreeNode) element;
			int size = node.children.size();
			treeViewer.setChildCount(element, size);
		}

		@Override
		public Object getParent(Object element) {
			return ((TreeNode) element).parent;
		}
	}

	/**
	 * Model for the viewer.
	 */
	private static class TreeNode {
		private String value;
		private final List<TreeNode> children = new ArrayList<TreeSnippet.TreeNode>();
		private final TreeNode parent;

		public TreeNode(TreeNode parent, String value) {
			this.parent = parent;
			this.value = value;
			if (parent != null) {
				parent.children.add(this);
			}
		}

		@Override
		public String toString() {
			return value;
		}
	}
}