code: public void put(K[] key, V value) {
          Node child = root.get(key[0]);
          if (child == null) {
              child = new Node(key[0]);
              root.put(key[0], child);
          }
          child.addChild(key, value, 1);
      }
docs: Add a key with associated value to the trie.
  @param key the key.
  @param value the value.