switch ( parents.size() ) {
case 0 :
BitSet zero = new BitSet();
if ( hasKey(zero) ) {
HierNode root = getNodeByKey(zero);
if ( root.getValue() != null ) {
fixedRoot = true;
HierNode previousRoot = root;
root = new HierNode( (Object) null );
root.addChild( previousRoot );
previousRoot.addParent( root );
root.setBitMask( zero );
propagate( previousRoot, freeBit( root ) );
add( root );