C#，List集合多重GroupBy

var data1 = _m.GetPurchase_Title(MasterId).FirstOrDefault();//表头
                var data2 = _m.GetPurchaseDt(MasterId);//明细

                var result = new
                {
                    PurNo = data1.MasterId,
                    ProviderName = data1.ProvideName,
                    Remark = data1.Remark,
                    SumCount = data1.preQty,
                    SumMoney = data1.OMoney,
                    Detail_style = data2.GroupBy(m => m.style).Select(g => new
                    {
                        style = g.Key,
                        Detail_Sku = g.Select(n => n)
                        .GroupBy(x => new { x.StyleName, x.SerialNo, x.AttribName, x.ClrName, x.Oprice })
                        .Select(t => new
                        {
                            preQty = t.Sum(b => b.preQty),
                            OPrice = t.Key.Oprice,
                            OMoney = t.Sum(b => b.OMoney),
                            StyleName = t.Key.StyleName,
                            SerialNo = t.Key.SerialNo,
                            AttribName = t.Key.AttribName,
                            ClrName = t.Key.ClrName,
                            Size = t.Select(v => v).GroupBy(z => z.SizeName).Select(k => k.Key + ":" + k.Sum(l => l.preQty).ToString())
                        })
                    })
                };

{
            "errmsg": "ok",
            "PurNo": "B201709270000019",
            "ProviderName": "外4Q-37615林志峰",
            "Remark": "这是一段牛逼的备注",
            "SumCount": 100,
            "SumMoney": 2400.00,
            "Detail_style": [{
                    "style": "10B73A33980",
                    "Detail_Sku": [{
                        "preQty": 8,
                        "OPrice": 100.00,
                        "OMoney": 2400.00,
                        "StyleName": "这是品名",
                        "SerialNo": "原厂编号",
                        "AttribName": "专柜",
                        "ClrName": "大红",
                        "SizebName": ["36:10", "37:10", "38:20", "L:30", "XLL:100"]
                    }, {
                        "SkuCount": 9,
                        "OPrice": 100.00,
                        "OMoney": 2400.00,
                        "StyleName": "这是品名",
                        "SerialNo": "原厂编号",
                        "AttribName": "专柜",
                        "ClrName": "绿",
                        "SizebName": ["X:10", "XX:10", "XXL:20", "L:30", "XLL:100"]
                    }]
                },
                {
                    "style": "20B73A33981",
                    "Detail_Sku": [{
                        "SkuCount": 10,
                        "OPrice": 100.00,
                        "OMoney": 2400.00,
                        "StyleName": "这是品名",
                        "SerialNo": "原厂编号",
                        "AttribName": "专柜",
                        "ClrName": "颜色",
                        "SizebName": ["X:10", "XX:10", "XXL:20", "L:30", "XLL:100"]
                    }, {
                        "SkuCount": 11,
                        "OPrice": 100.00,
                        "OMoney": 2400.00,
                        "StyleName": "这是品名",
                        "SerialNo": "原厂编号",
                        "AttribName": "专柜",
                        "ClrName": "颜色",
                        "SizebName": ["X:10", "XX:10", "XXL:20", "L:30", "XLL:100"]
                    }]
                }
            ]
        }