I'd hold the consolidated date using a hash the following way

my $array = [[apple, a1], [apple, a2], [apple, a3]]; 
my %hash = ();
foreach (@{$array}) {
    $hash{$_->[0]} = [] unless defined($hash{$_->[0]});
    push (@{$hash{$_->[0]}}, $_->[1]); 
}
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resulting in %hash == ( apple => [ a1, a2, a3 ], )

Update:Another way to get your whished for result [[apple, a1, a2, a3 ]]:

use List::Util qw(reduce);

my $array = [[apple, a1], [apple, a2], [apple, a3]]; 
my $result = [];
unshift(@$array, []);
push @$result, reduce { 
    push(@$a, $b->[0]) unless exists $a->[0];
    push(@$a, $b->[1]); 
    $a;
} @$array;
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