@structure = (
    { ... },
    [
        { ... },
        { ... },
    ],
    [
        { ... },
        { ... },
    ],
    [
        { ... },
        { ... },
    ],
);

##</code><code>##

my @structure = ( $hashref_from_first );
foreach @query {
  ...
  push @structure, []
  foreach @subquery {
     ...
     push @structure->[0], $hashref; 
  }
}