default boolean isSibling(final Tree<?, ?> node) {
		return identical(requireNonNull(node)) ||
			parent().equals(node.parent());
	}
Test if the given {@code node} is a sibling of {@code this} node.

@param node node to test as sibling of this node
@return {@code true} if the {@code node} is a sibling of {@code this}
        node
@throws NullPointerException if the given {@code node} is {@code null}
jenetics.ext/src/main/java/io/jenetics/ext/util/Tree.java