Expand description
Returns the parent of a node.
Examples
assert_eq!(flat_tree::index(1, 0), 1);
assert_eq!(flat_tree::index(1, 1), 5);
assert_eq!(flat_tree::index(2, 0), 3);
assert_eq!(flat_tree::parent(0), 1);
assert_eq!(flat_tree::parent(2), 1);
assert_eq!(flat_tree::parent(1), 3);