code: public static <T> T root(TreeDef.Parented<T> treeDef, T node) {
  		T lastParent;
  		T parent = node;
  		do {
  			lastParent = parent;
  			parent = treeDef.parentOf(lastParent);
  		} while (parent != null);
  		return lastParent;
  	}
docs: Returns the root of the given tree.