Is there a better way to insert into a table than below?

I have a need where I need to use two queries which differ from each other by a single condition.
Eg.

SELECT * 
  FROM table
 WHERE attribute1 = 'Y';

SELECT * 
  FROM table
 WHERE attribute1 IS NULL;

My need is to insert data from these two queries into a single table the only condition being that the data from the first query should go in first and then the second query.
I can obviously run the first query first insert and run the second query and then insert again.
My question is there a better way to do that?

To me, it looks like

SELECT *
  FROM your_table
 WHERE (   attribute1 = 'Y'
        OR attribute1 IS NULL);

A (worse) alternative would be to union (all) these two selects:

SELECT *
  FROM your_table
 WHERE attribute1 = 'Y'
UNION ALL
SELECT *
  FROM your_table
 WHERE attribute1 IS NULL;

If the # of rows you are requesting is significant percentage of the table, then no, there is no better way to do that. If you require that the first insert happen before the second insert, then the way to guarantee that is to do each in order, as separate SQL statements. Any combining of the two leads to the possibility of mixing the results. Sure, you can force ordering with ORDER BY, you can make assumptions about UNION ALL (but with concurrent union PX in recent versions, this is not a safe assumption), but these are all inferior methods to simply using two statements. A sort can be quite expensive.

If however you are querying a massive table and each of your queries expects only a small percent of rows, then the cost of a sort might be cheaper than two table scans. In that case, you can combine the queries and force the order with an explicit ORDER BY:

SELECT *
  FROM your_table
 WHERE NVL(attribute1,'Y') = 'Y'
ORDER BY DECODE(attribute1,'Y',1,2)

But unless this is necessary to achieve the performance goals at hand, it is less clear and therefore not a great way to code. Most likely in your situation, using two statements is best from all perspectives.