Recursively:

use strict;
use warnings;
use Data::Dumper;

sub set_hash
{
   my $href = shift;
   my $val  = shift;
   my $key  = shift;
   if( @_ ) {
       $href->{$key} = {} if not exists $href->{$key};
       set_hash( $href->{$key}, $val, @_ );
   } else {
       $href->{$key} = $val;
   }
}

my %h;
set_hash(\%h, 42, 'a', 'b', 'c');
set_hash(\%h, 69, 'x', 'y', 'z', 'aa' );
print Dumper(\%h);
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