docs: public void insertNodeAfter(Node insert, Node after, int direction) {
          if (isSplitterDirection(direction)) {
              double split = getSplit(after) / 2;
              setSplit(after, split);
              addChild(insert, children.indexOf(after) + 1, split);
          }
          else {
              pushDown(after, after, insert);
          }
          notifyStateChange();
      }