0 - 1 of 1 tags for case insert stored procedure

I have an insert statement:
INSERT INTO tbl1 (Col1)
SELECT
    CASE
        WHEN Col1 = 'a' THEN 'TRUE'
        ELSE 'FALSE'
    END
FROM tbl2;
This works as expected.  For every row in tbl2, 1 row gets inserted into tbl1 with a Col1 value of 'TRUE' or 'FALSE'