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
if (includeChildren && getExpanded(item)) {
            Item[] children = getItems(item);
            if (children != null && children.length > 0) {
                return children[0];
            }
        }
        
        
        Item parent = getParentItem(item);
        if (parent == null) {
            return null;
        }
        Item[] siblings = getItems(parent);
        if (siblings != null && siblings.length <= 1) {
            return getNextItem(parent, false);
        }
        for (int i = 0; i < siblings.length; i++) {
            if (siblings[i] == item && i < (siblings.length - 1)) {
                return siblings[i + 1];
            }
        }
        return getNextItem(parent, false);
    }
    /**
     * Returns the parent item of the given item in the tree, or <code>null</code>
     * if there is parent item.
     * 
     * @param item
     *           the item
     * @return the parent item, or <code>null</code> if none