#! perl -slw
use strict;

my %ini;
my( $product, $feature );
while( <DATA> ) {
    chomp;
    if( /\s+(\S+)=(\S+)/ ) {
        $ini{ $product // die "Malformed ini at:$." }
            { $feature // 'none' }
            { $1 } = $2;
        push @{ $ini{ $product }{ $feature // 'none' }{ order } }, $1;
    }
    elsif( /^PROD/ ) {
        push @{ $ini{ $product }{ order } }, 'none'
            if $product and not exists $ini{ $product }{ order };
        $product = $_;
        push @{ $ini{ order } }, $product;
        undef $feature;
    }
    else {
        /^\s+(\S+)/ and $feature = $1;
        push @{ $ini{ $product }{order} }, $feature;
    }
}

for my $product ( @{ $ini{ order } } ) {
    print $product;
    for my $feature ( @{ $ini{ $product }{ order } } ) {
        print "\t", $feature if $feature ne 'none';
        for my $type ( @{ $ini{ $product }{ $feature }{ order } } ) {
            print "\t\t$type=$ini{ $product }{ $feature }{ $type }";
        }
    }
}

__DATA__
PRODUCT1
   FEATURE1_PRODUCT1
      PROPERTY1_FEATURE1_PRODUCT1=VALUE1
      PROPERTY2_FEATURE1_PRODUCT1=VALUE2
      PROPERTY3_FEATURE1_PRODUCT1=VALUE3
PRODUCT2
      PROPERTY1_PRODUCT2=VALUE1
      PROPERTY2_PRODUCT2=VALUE2
PRODUCT3
   FEATURE1_PRODUCT3
      PROPERTY1_FEATURE1_PRODUCT3=VALUE1
      PROPERTY2_FEATURE1_PRODUCT3=VALUE2
      PROPERTY3_FEATURE1_PRODUCT3=VALUE3
   FEATURE2_PRODUCT3
      PROPERTY1_FEATURE1_PRODUCT3=VALUE1
   FEATURE3_PRODUCT3
      PROPERTY1_FEATURE1_PRODUCT3=VALUE1
      PROPERTY2_FEATURE1_PRODUCT3=VALUE2
      PROPERTY3_FEATURE1_PRODUCT3=VALUE3
PRODUCT4
      PROPERTY1_PRODUCT4=VALUE1
      PROPERTY2_PRODUCT4=VALUE2
PRODUCT5