Saving JSON file to SQL Server Database tables

As JSON case sensitive please check your schema definition and sample data. I see a discrepancy between the definition of the tables, their contents and your JSON

All scripts tested on MS SQL Server 2016

I used a temporary table variable in this script, but you can do without it. See an example in SQL Fiddle

-- JSON -> hierarchy table
DECLARE @ExpectedJSON NVARCHAR(MAX) = '
{
    "condition": "and",
    "rules": [
      {
        "field": "26",
        "operator": "=",
        "value": "TEST1"
      },
      {
        "field": "36",
        "operator": "=",
        "value": "TEST2"
      },
      {
        "condition": "or",
        "rules": [
          {
            "field": "2",
            "operator": "=",
            "value": 100
          },
          {
            "field": "3",
            "operator": "=",
            "value": 12
          },
          {
            "condition": "or",
            "rules": [
              {
                "field": "12",
                "operator": "=",
                "value": "CA"
              },
              {
                "field": "12",
              "operator": "=",
              "value": "AL"
            }
          ]
        }
      ]
    }
  ]
}
'

DECLARE @TempRuleset AS TABLE 
(RulesetID          BIGINT NOT NULL PRIMARY KEY,
 condition          VARCHAR(50) NOT NULL,
 ParentRuleSetID    BIGINT NOT NULL,
 RulesJSON          NVARCHAR(MAX)
)

;WITH ParseRuleset AS (
    SELECT  1 AS RulesetID,
            p.condition,
            p.rules,
            0 AS ParentRuleSetID
    FROM OPENJSON(@ExpectedJSON, '$') WITH (
        condition   VARCHAR(50),
        rules       NVARCHAR(MAX) AS JSON
    ) AS p

    UNION ALL

    SELECT  RulesetID + 1,
            p.condition,
            p.rules,
            c.RulesetID AS ParentRuleSetID
    FROM ParseRuleset AS c
        CROSS APPLY OPENJSON(c.rules) WITH (
            condition   VARCHAR(50),
            rules       NVARCHAR(MAX) AS JSON
        ) AS p
    where
        p.Rules IS NOT NULL
)

INSERT INTO @TempRuleset (RulesetID, condition, ParentRuleSetID, RulesJSON)
SELECT  RulesetID,
        condition,
        ParentRuleSetID,
        rules
FROM ParseRuleset

 -- INSEERT INTO Ruleset ...
SELECT RulesetID,
        condition,
        ParentRuleSetID,
        RulesJSON
FROM @TempRuleset

-- INSERT INTO Rules ...
SELECT  RulesetID,
        field,
        operator,
        value
FROM @TempRuleset tmp
     CROSS APPLY OPENJSON(tmp.RulesJSON) WITH (
                field       VARCHAR(MAX),
                operator    VARCHAR(MAX),
                value       VARCHAR(MAX)
             ) AS p
WHERE   p.field IS NOT NULL

SQL Fiddle

Hierarchy tables -> JSON:

CREATE TABLE Ruleset
(RulesetID       BIGINT IDENTITY(1, 1) NOT NULL PRIMARY KEY,
 condition       VARCHAR(50) NOT NULL,
 ParentRuleSetID BIGINT NULL
);
GO
CREATE TABLE Rules
(RuleID     BIGINT IDENTITY(1, 1) NOT NULL PRIMARY KEY,
 field      VARCHAR(MAX) NOT NULL,
 operator   VARCHAR(MAX) NOT NULL,
 value      VARCHAR(MAX) NOT NULL,
 RulesetID  BIGINT NULL FOREIGN KEY REFERENCES Ruleset(RulesetID)
);

INSERT INTO Ruleset values  
    ('and',0),
    ('or',1),
    ('or',2) 

INSERT INTO Rules values  
    ('26','=','TEST1',1),
    ('36','=','TEST2',1),
    ('2','=','100',2),
    ('3','=','12',2),
    ('12','=','CA',3),
    ('12','=','AL',3)

-- hierarchy table -> JSON
;WITH GetLeafLevel AS 
(
    SELECT  Ruleset.RulesetID,
            Ruleset.condition,
            Ruleset.ParentRuleSetID,
            1 AS lvl,
            (   SELECT  field,
                        operator,
                        value
                FROM    Rules
                WHERE   Rules.RulesetID = Ruleset.RulesetID
                FOR JSON AUTO, WITHOUT_ARRAY_WRAPPER 
            ) AS JSON_Rules
    FROM    Ruleset
    WHERE   ParentRuleSetID = 0
    UNION ALL
    SELECT  Ruleset.RulesetID,
            Ruleset.condition,
            Ruleset.ParentRuleSetID,
            GetLeafLevel.lvl + 1,
            (   SELECT  field,
                        operator,
                        value
                FROM    Rules
                WHERE   Rules.RulesetID = Ruleset.RulesetID
                FOR JSON AUTO, WITHOUT_ARRAY_WRAPPER 
            )
    FROM    Ruleset
            INNER JOIN GetLeafLevel ON Ruleset.ParentRuleSetID = GetLeafLevel.RulesetID
),
-- SELECT * FROM GetLeafLevel       -- debug 
ConcatReverseOrder AS 
(
    SELECT  GetLeafLevel.*,
            CONCAT('{"condition":"',
                    GetLeafLevel.condition,
                    '","rules":[',
                    GetLeafLevel.JSON_Rules,
                    ']}'
                    ) AS js
    FROM    GetLeafLevel
    WHERE   GetLeafLevel.lvl = (SELECT MAX(lvl) FROM GetLeafLevel)
    UNION ALL
    SELECT  GetLeafLevel.*,
            CONCAT('{"condition":"',
                            GetLeafLevel.condition,
                            '","rules":[',
                            GetLeafLevel.JSON_Rules,
                            ',',
                            ConcatReverseOrder.js,
                            ']}'
                            ) AS js
    FROM    GetLeafLevel
            INNER JOIN ConcatReverseOrder ON GetLeafLevel.RuleSetID = ConcatReverseOrder.ParentRuleSetID 
)
-- SELECT * FROM ConcatReverseOrder     -- debug 

SELECT  js
FROM    ConcatReverseOrder
WHERE   ParentRuleSetID = 0

SQL Fiddle