public void removeChild(final T_TREE_NODE node) {
        final T_TREE_NODE parent = parents.remove(node);
        if (parent != null) {
            final List<T_TREE_NODE> children = getChildrenList(parent);
            if (children != null) {
                children.remove(node);
            }
        }
    }
@param parentNode [hasNode(parentNode)]
@param node       [!hasNode(node)]
stroom-core-client-widget/src/main/java/stroom/widget/htree/client/treelayout/util/DefaultTreeForTreeLayout.java