code: protected void addChild(Node child, int index, double split) {
          children.add(index, child);
          nodeSplits.put(child, split);
          child.setParent(this);
      }
docs: Adds a child of this node.
  @param child The child node to be added
  @param index The position of the child node.
  @param split The amount/weighting of parent node that the child node should
  receive