code: function create(key, value) {
    if (!Buffer.isBuffer(key)) {
      throw new TypeError('expected buffer')
    }
  
    return {
      key,
      value,
      left: null,
      right: null,
      height: 0
    }
  }
docs: create new AVL tree node
  @returns {{key: null, value: null, height: number, left: null, right: null}}