MySQL query tree structure method

CREATE TABLE `tree` (
  `id` bigint(11) NOT NULL,
  `pid` bigint(11) NULL DEFAULT NULL,
  `name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;
INSERT INTO `tree` VALUES (1, 0, '中国');
INSERT INTO `tree` VALUES (2, 1, 'Sichuan Province');
INSERT INTO `tree` VALUES (3, 2, 'Chengdu');
INSERT INTO `tree` VALUES (4, 3, 'Wuhou District');
INSERT INTO `tree` VALUES (5, 4, 'Red Archway');
INSERT INTO `tree` VALUES (6, 1, 'Guangdong Province');
INSERT INTO `tree` VALUES (7, 1, 'Zhejiang Province');
INSERT INTO `tree` VALUES (8, 6, 'Guangzhou');

CREATE FUNCTION `GET_CHILD_NODE`(rootId varchar(100))   
RETURNS varchar(2000)  
BEGIN   
DECLARE str varchar(2000);  
DECLARE cid varchar(100);   
SET str = '$';   
SET cid = rootId;   
WHILE cid is not null DO   
    SET str = concat(str, ',', cid);   
    SELECT group_concat(id) INTO cid FROM tree where FIND_IN_SET(pid, cid);   
END WHILE;   
RETURN str;   
END

select * from tree where FIND_IN_SET(id, GET_CHILD_NODE(2)); 

CREATE FUNCTION `GET_PARENT_NODE`(rootId varchar(100))   
RETURNS varchar(1000)   
BEGIN   
DECLARE fid varchar(100) default '';   
DECLARE str varchar(1000) default rootId;   
  
WHILE rootId is not null do   
    SET fid =(SELECT pid FROM tree WHERE id = rootId);   
    IF fid is not null THEN   
        SET str = concat(str, ',', fid);   
        SET rootId = fid;   
    ELSE   
        SET rootId = fid;   
    END IF;   
END WHILE;   
return str;  
END

select * from tree where FIND_IN_SET(id, GET_PARENT_NODE(5)); 

public class TreeNodeDTO {
    
    private String id;
    private String parentId;
    private String name;
    private List<TreeNodeDTO> children = new ArrayList<>();
    public void add(TreeNodeDTO node) {
        if ("0".equals(node.parentId)) {
            this.children.add(node);
        } else if (node.parentId.equals(this.id)) {
            this.children.add(node);
        } else {
         	//Recursively call add() to add child nodes for (TreeNodeDTO tmp_node : children) {
                tmp_node.add(node);
            }
        }
    }
 }

List<TreeNodeDTO> list = dbMapper.getNodeList();
ArrayList<TreeNodeDTO> rootNodes = new ArrayList<>();
Map<Integer, TreeNodeDTO> map = new HashMap<>();
for (TreeNodeDTO node : list) {
    map.put(node.getId(), node);
    Integer parentId = node.getParentId();
    // Determine whether there is a parent node (if there is no parent node, it is a parent menu)
    if (parentId.equals('0')){
        rootNodes.add(node);
        // Find the menu that is not the parent menu and includes its parent menu ID in the collection
    } else if (map.containsKey(parentId)){
        map.get(parentId).getChildren().add(node);
    }
}

START WITH CONNECT BY PRIOR

CREATE TABLE `company_inf` (
  `ID` varchar(32) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  `NAME` varchar(255) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  `PARENT_ID` varchar(32) COLLATE utf8mb4_unicode_ci DEFAULT NULL
)

INSERT INTO company_inf VALUES ('1','General Manager Wang Damazi','1');
INSERT INTO company_inf VALUES ('2','R&D Manager Liu Daquezi','1');
INSERT INTO company_inf VALUES ('3','Sales Manager Ma Erlangzi','1');
INSERT INTO company_inf VALUES ('4','Finance Manager Zhao Santuozi','1');
INSERT INTO company_inf VALUES ('5','Secretary Employee J','1');
INSERT INTO company_inf VALUES ('6','R&D Team Leader Wu Dabangchui','2');
INSERT INTO company_inf VALUES ('7','Zheng Laoliu, head of R&D Group 2','2');
INSERT INTO company_inf VALUES ('8','Salesperson G','3');
INSERT INTO company_inf VALUES ('9','Salesperson H','3');
INSERT INTO company_inf VALUES ('10','Financial Personnel I','4');
INSERT INTO company_inf VALUES ('11','Developer A','6');
INSERT INTO company_inf VALUES ('12','Developer B','6');
INSERT INTO company_inf VALUES ('13','Developer C','6');
INSERT INTO company_inf VALUES ('14','Developer D','7');
INSERT INTO company_inf VALUES ('15','Developer E','7');
INSERT INTO company_inf VALUES ('16','Developer F','7');

  SELECT *
  FROM T_PORTAL_AUTHORITY
  START WITH ID='1'
  CONNECT BY PRIOR ID = PARENT_ID

CREATE FUNCTION getChild(parentId VARCHAR(1000))
RETURNS VARCHAR(1000)
BEGIN
    DECLARE oTemp VARCHAR(1000);
    DECLARE oTempChild VARCHAR(1000);
    SET oTemp = '';
    SET oTempChild = parentId;
    WHILE oTempChild is not null DO
        IF oTemp != '' THEN
            SET oTemp = concat(oTemp,',',oTempChild);
        ELSE
            SET oTemp = oTempChild;
        END IF;
        SELECT group_concat(ID) INTO oTempChild FROM company_inf where parentId<>ID and FIND_IN_SET(parent_id,oTempChild)>0;
    END WHILE;
RETURN oTemp;
END

SELECT * FROM company_inf WHERE FIND_IN_SET(ID,getChild('2'));