my %hash;
while(<DATA>){
    chomp;
    my @line = split /\t/;
    my $first = shift @line;
    $hash{$first}{$_}++ for @line;
}
foreach( sort keys %hash ){
    print STDOUT "$_\t".join("\t", sort keys %{$hash{$_}})."\n";
}
__DATA__
text1   text-a  text-a  text-b  text-a
text1   text-c
text2   text-a  text-b
text2   text-b  text-d
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All I changed was the push line and the print line. Output:

text1   text-a  text-b  text-c
text2   text-a  text-b  text-d
[download]