@Override
	public FlatTreeNode<V> root() {
		return nodeAt(0);
	}
Returns the root of the tree that contains this node. The root is the
ancestor with no parent. This implementation has a runtime complexity
of O(1).

@return the root of the tree that contains this node
jenetics.ext/src/main/java/io/jenetics/ext/util/FlatTreeNode.java