How to show child items in a post field

Hello,
i have a post field like:

array(
	'name'	        => __('Page'),
	'placeholder'   => sprintf(__('Select %s'), __('Page')),
	'id'	        => 'book_page_id',
	'type'	        => 'post',
	'post_type'     => 'page',
	'field_type'    => 'select_tree',
	'query_args'    => array(
		'post_status' => 'publish',
		'posts_per_page' => - 1,
	)
)

But the field only show me the parent pages, not the child pages.
How can i config this field, to show me all pages (with child pages)?

Thank you very much