Android Gsonでjsonデータをパースする

Gsonを使って配列型Json(JsonArray)をList型オブジェクトにパース
しようと思っているのですが、うまくいかず困っています。
どこらへんに問題があるのかアドバイスいただけると助かります

//json取得部分
 StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                        Gson gson = new Gson();
                        Type type = new TypeToken<List>(){}.getType();
                        List<ProblemSet> list = gson.fromJson(response,type);
                        Log.v("Test",String.valueOf(list));
                    }
                }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                Log.e("test", "onErrorResponse: " );
            }
        });

//json
{
  "problems": [
    {
      "question": {
        "id": 1,
        "content": "1 + 1 =",
        "correct_option_id": 2
      },
      "options": [
        {
          "id": 1,
          "content": "1",
          "correct": false
        },
        {
          "id": 2,
          "content": "2",
          "correct": true
        },
        {
          "id": 3,
          "content": "3",
          "correct": false
        },
        {
          "id": 4,
          "content": "4",
          "correct": false
        }
      ]
    },
    
    {
        "problem": {
          "id": 2,
          "content": "2 + 3 =",
          "correct_option_id": 2
        },
        "options": [
          {
            "id": 1,
            "content": "4",
            "correct": false
          },
          {
            "id": 2,
            "content": "5",
            "correct": true
          },
          {
            "id": 3,
            "content": "6",
            "correct": false
          },
          {
            "id": 4,
            "content": "7",
            "correct": false
          }
        ]
      }
  ]
}

//Gsonに整形
public class ProblemSet {

    private Question question;

    public Question getQuestion() {
        return question;
    }

    //1.questionのクラスを作成
    private class Question{
        private int id;
        private String content;
        private int correct_option_id;

        public int getId() {
            return id;
        }

        public void setId(int id) {
            this.id = id;
        }

        public String getContent() {
            return content;
        }

        public void setContent(String content) {
            this.content = content;
        }

        public int getCorrect_option_id() {
            return correct_option_id;
        }

        public void setCorrect_option_id(int correct_option_id) {
            this.correct_option_id = correct_option_id;
        }
    }
}