SELECT 1 ord,   'aaa' AS tag_name,   'aaa' tag_value,    NULL AS id,     NULL AS id_par,     NULL as attr_value                  FROM DUAL UNION ALL
SELECT 2 ord,   'bbb' AS tag_name,   NULL tag_value,     1 AS id,        NULL AS id_par,     NULL as attr_value                  FROM DUAL UNION ALL
SELECT 3 ord,   'ccc' AS tag_name,   'ccc' tag_value,    2 AS id,        1 AS id_par,        'atr1="1" atr2="2"' as attr_value   FROM DUAL UNION ALL
SELECT 4 ord,   'ddd' AS tag_name,   'ddd' tag_value,    3 AS id,        1 AS id_par,         NULL as attr_value                 FROM DUAL

<aaa>aaa</aaa>
<bbb>
 <ccc atr1="1" atr2="2">ссс</ccc>
 <ddd>ddd</ddd>
</bbb>

SELECT DBMS_XMLGEN.getxmltype(DBMS_XMLGEN.newContextFromHierarchy('
WITH test AS 
(
SELECT 1 ord,   ''aaa'' AS tag_name,   ''aaa'' tag_value,    NULL AS id,     NULL AS id_par,     NULL as attr_value                  FROM DUAL UNION ALL
SELECT 2 ord,   ''bbb'' AS tag_name,   NULL tag_value,     1 AS id,        NULL AS id_par,     NULL as attr_value                  FROM DUAL UNION ALL
SELECT 3 ord,   ''ccc'' AS tag_name,   ''ccc'' tag_value,    2 AS id,        1 AS id_par,        ''atr1="1" atr2="2"'' as attr_value   FROM DUAL UNION ALL
SELECT 4 ord,   ''ddd'' AS tag_name,   ''ddd'' tag_value,    3 AS id,        1 AS id_par,         NULL as attr_value                 FROM DUAL
)
SELECT lvl,
       XMLELEMENT ( evalname tag_name,                                    
                    XMLAttributes(attr_value AS "attr"),
                    tag_value) XML
  FROM
(
  SELECT LEVEL AS lvl,
         tag_name,
         tag_value,
         attr_value,
         ord               
    FROM test        
   START WITH id_par is null
 CONNECT BY PRIOR id = id_par
)
ORDER BY ord
')) AS xml FROM dual

<ccc attr="atr1=&quot;1&quot; atr2=&quot;2&quot;">ccc</ccc> 

<ccc atr1="1" atr2="2"></ccc>