Parsing Bitcoin Script OP_IF OP_ELSE expressions

//original script 
//0 IF 1 IF RETURN ELSE RETURN ELSE RETURN ENDIF ELSE 1 IF 1 ELSE RETURN ELSE 1 ENDIF ELSE RETURN ENDIF ADD 2 EQUAL

//OP_IF RULE
//If the top stack value is not 0, the statements are executed. The top stack value is removed.

//OP_ELSE RULE
//If the preceding OP_IF or OP_NOTIF or OP_ELSE was not executed then these statements are and 
//if the preceding OP_IF or OP_NOTIF or OP_ELSE was executed then these statements are not.
0
OP_IF 
  1
  OP_IF
    OP_RETURN
  OP_ELSE
    OP_RETURN
  OP_ELSE
    OP_RETURN
  OP_ENDIF

OP_ELSE
  1
  OP_IF 
    1
  OP_ELSE
    OP_RETURN
  OP_ELSE
    1
  OP_ENDIF

OP_ELSE
  OP_RETURN
  
OP_ENDIF

OP_ADD
2
OP_EQUAL