# With strictures:
use strict;
use warnings;
use Data::Dump 'pp';

my %hash;
$hash{tree} = 4;
$hash{tree}->{apple} = 6; 

pp \%hash;

__END__
Can't use string ("4") as a HASH ref while "strict refs" in use at G:\x.pl line 7.

##</code><code>##

# Without strictures:
use warnings;
use Data::Dump 'pp';

my %hash;
$hash{tree} = 4;
$hash{tree}->{apple} = 6; 

pp \%hash;

__END__
{ tree => 4 }