default Iterator<T> postorderIterator() {
		return new TreeNodePostorderIterator<>(self());
	}
Return an iterator that traverses the subtree rooted at {@code this}
node in post-order. The first node returned by the iterator is the
leftmost leaf.  This is the same as a depth-first traversal.

@see #depthFirstIterator
@see #preorderIterator
@return an iterator for traversing the tree in post-order
jenetics.ext/src/main/java/io/jenetics/ext/util/Tree.java