insert(data) {
    if (!Array.isArray(data)) {
      return this._insertRecord(data);
    } else {
      return map(data, (attrs) => this._insertRecord(attrs));
    }
  }
Inserts `data` into the collection. `data` can be a single object
    or an array of objects. Returns the inserted record.

    ```js
    // Insert a single record
    let link = db.users.insert({ name: 'Link', age: 173 });

    link;  // { id: 1, name: 'Link', age: 173 }

    // Insert an array
    let users = db.users.insert([
      { name: 'Zelda', age: 142 },
      { name: 'Epona', age: 58 },
    ]);

    users;  // [ { id: 2, name: 'Zelda', age: 142 }, { id: 3, name: 'Epona', age: 58 } ]
    ```

    @method insert
    @param data
    @public