Bug 93360 [Viewers] getChild still used in indexForElement
indexForElement() in AbstractTreeViewer still uses getChild() and not getChildren(). This should probably also change to using getChildren() and do the same thing as insertionPosition().
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java
* @return Widget
     */
    protected Widget internalExpand(Object element, boolean expand) {
        if (element == null)
            return null;
        Widget w = internalGetWidgetToSelect(element);
        if (w == null) {
            if (equals(element, getRoot())) { 
                return null;
            }
            
            ITreeContentProvider cp = (ITreeContentProvider) getContentProvider();
            if (cp == null) {
                return null;
            }
            Object parent = cp.getParent(element);
            if (parent != null) {
                Widget pw = internalExpand(parent, expand);
                if (pw != null) {
                    
                    createChildren(pw);
                    
                    if (pw instanceof Item) {
                        Item item = (Item) pw;
                        if (expand)
                            setExpanded(item, true);
                        w = internalFindChild(item, element);
                    }
                }
            }