function readNode() {
        if (i >= items.length) {
            return null;
        }
        const start = i;
        const height = items[start].listHeight;
        i++;
        while (i < items.length && items[i].listHeight === height) {
            i++;
        }
        if (i - start >= 2) {
            return concat23TreesOfSameHeight(start === 0 && i === items.length ? items : items.slice(start, i), false);
        }
        else {
            return items[start];
        }
    }
Reads nodes of same height and concatenates them to a single node.