DECLARE

  qryctx DBMS_XMLGEN.ctxhandle;
  v_date date;
  xmldoc CLOB;

BEGIN

qryctx :=
    DBMS_XMLGEN.newcontextfromhierarchy
            ('SELECT level,
                 XMLElement("child",XMLAttributes(level as "level",child_alias as  "alias" )
            
                                                 )
            FROM xmlhier
            START WITH parent_alias is null
            CONNECT BY PRIOR child_alias=parent_alias
            ');
   
  xmldoc := DBMS_XMLGEN.getXML(qryctx);
  DBMS_OUTPUT.put_line(xmldoc);
  DBMS_XMLGEN.closecontext(qryctx);
END;


<?xml version="1.0"?>
<child level="1" alias="A61X">
  <child level="2" alias="CM10"/>
  <child level="2" alias="CM11"/>
  <child level="2" alias="ZVMD"/>
  <child level="2" alias="ZVMK">
    <child level="3" alias="CM12"/>
    <child level="3" alias="CM1E">
      <child level="4" alias="CM13"/>
      <child level="4" alias="CM1F"/>
    </child>
  </child>
</child>