code: private void addChildNode(Node<V> parent,
  			      String key,
  			      int transitionCharIndex,
  			      V value) {
  	char transitionChar = key.charAt(transitionCharIndex);
  	Node<V> child = new Node<V>(key, transitionCharIndex + 1, value);
  	parent.addChild(transitionChar, child);
  	size++;
      }
docs: Adds a child {@link Node} node to the provided parent using the {@code
  char} at the transition index to determine the link.
  
  @param parent the node to which the child will be added
  @param key the key that is being mapped to the provided value
  @param transitionCharIndex the character index in {@key} to which the new
  node should be linked from the parent node
  @param value the value being mapped to the provided key