default boolean isDescendant(final Tree<?, ?> node) {
		return requireNonNull(node).isAncestor(this);
	}
Return {@code true} if the given {@code node} is a descendant of
{@code this} node. If the given {@code node} is {@code null},
{@code false} is returned. This operation is at worst {@code O(h)} where
{@code h} is the distance from the root to {@code this} node.

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