As an extension of the standard だけでなく, meaning ‘not only, but also’, adding the 副助詞（ふくじょし） (adverbial particle) も to the (B) part of a sentence will place extra emphasis on the thing that is being included in the same category as (A).
だけ itself is a 副助詞（ふくじょし）, so will primarily follow nouns. After this, the negative conjunctive form of the 助動詞（じょどうし） (auxiliary verb) だ (でなく) will create the ‘not only’ meaning.

• アメリカだけではなく、韓国（かんこく）とチリにも行（い）った事（こと）があります。
  Not only the US, I have also been to Korea and Chile.
• 日本（にほん）は地震（じしん）だけでなく、台風（たいふう）も多（おお）いです。
  Not only are there earthquakes in Japan, there are also many typhoons.

て is not strictly required as part of this structure, but will help to create a far more natural ‘separation’ between (A) and (B) when it is used.

• 漫画（まんが）は子供（こども）だけではなくて、大人（おとな）にも人気（にんき）があります。
  Not only is manga popular amongst children, it is popular among adults too.

Either じゃなく or じゃなくて may also be used, as is the case with all でなく and ではなく based grammar structures.

• お年玉（としだま）は子供（こども）だけじゃなく、大人（おとな）ももらえたらいいのにね。
  Don't you think it would be nice if adults also got money during new years and not just kids?
• 遊園地（ゆうえんち）だけじゃなくて動物園（どうぶつえん）にも連（つ）れて行（い）ってほしい。
  Not only the amusement park, I also want you to take me to the zoo.