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sub tree_data {
  my ( $old_data, $key_name, $next_group, @remaining_keys ) = @_;
...

  return \@new_data;
}

my $input = [
  {
...
    'other_data' => '123456789',
  },
];

my $output = [
  {
...
    ],
  },
];

# ...to generate the output example from above...
my $output = tree_data( $input, 'team', 'employees' );
...
my $output = tree_data(
  $input, 'team', 'employees', 'employee', 'work_days'
);