Bug 38782 TreeViewer add calls a refresh
Our implementation of TreeViewer.add is naive and can all a refresh of the entire tree. It should be more like TableViewer.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java
*/
	protected abstract Item getParentItem(Item item);
	/**
	 * Returns the item before the given item in the tree, or
	 * <code>null</code> if there is no previous item.
	 *
	 * @param item the item
	 * @return the previous item, or <code>null</code> if none
	 */
	protected Item getPreviousItem(Item item) {
		 
		
		Item parent = getParentItem(item);
		if (parent == null) {
			return null;
		}
		Item[] siblings = getItems(parent);
		if (siblings.length == 0 || siblings[0] == item) {
			return parent;
		}
		Item previous = siblings[0];
		for (int i = 1; i < siblings.length; i++) {
			if (siblings[i] == item) {
				return rightMostVisibleDescendent(previous);
			}
			previous = siblings[i];
		}
		return null;
	}
	/* (non-Javadoc)