find

        fn find(self: Self, key: Key, parent_ref: *?*Node) ?*Node {
            var node = self.root;
            parent_ref.* = null;

            // basic binary search while tracking the parent.
            while (node) |current| {
                const order = compare(key, current.key);
                if (order == .eq) break;

                parent_ref.* = current;
                node = current.children[@intFromBool(order == .gt)];
            }

            return node;
        }