Is something like this what you want?

use strict;
use warnings;
use feature 'say';

{
    package Tree;
    use Moose;
    has health_level => (
        is      => 'rw',
        isa     => 'Int',
    );
    
    sub grow_leaf {
        my $self = shift;
        Leaf->new(tree => $self); # pass $self on to child
    }
}

{
    package Leaf;
    use Moose;
    has tree => (
        is      => 'bare',
        handles => ['health_level'],
    );
}


my $t = Tree->new(health_level => 100);
my $l = $t->grow_leaf;

say $l->health_level;   # 100

$t->health_level(90);

say $l->health_level;   # 90
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