I use https://github.com/nyeholt/silverstripe-multivaluefield for my product $size values.
How to display these values ​​in a template?

public static $db = array(
		'Size'  => 'MultiValueField'
}
$sourceSize = array( 
							"12м." => "12м. (74-80см)",
							"18м." => "18м. (80-86см)",
							"2г."  => "2    (86-98см)"
				);
		
		$fields->addFieldToTab('Root.Main', new MultiValueCheckboxField('Size', 'Размер',$source = $sourceSize));

$SizeValue show to me a:4:{s:5:"12м.";s:5:"12м.";s:5:"18м.";s:5:"18м.";s:4:"2г.";s:4:"2г.";s:4:"4г.";s:4:"4г.";}
how to navigate through an array $Size?

<% loop Size %>$Value
<% end_loop %>

Based on https://github.com/silverstripe-australia/silverstripe-multivaluefield#basic-usage it should be iterating over $Size.Items