Roy Tanck

Hooks into WordPress core function <code>wp_list_pages</code>, and removes pages from the generated list that are not part of the 
current navigation path. This creates an accordion navigation effect, and is an alternative approach to the CSS-based 
way suggested in the <a href="https://codex.wordpress.org/Function_Reference/wp_list_pages#Markup_and_styling_of_page_items" rel="nofollow ugc">Codex</a>.
By removing unneeded HTML elements server-side, page size is reduced, and client-side rendering will usually be faster. 
This is especially true for older browsers, and sites with a large number of published pages.
This plugin is intended to be used with the “pages” widget that comes with WordPress, or any navigation element that uses 
wp_list_pages.
There are two ways the plugin can apply the filter.
<ol>
<li>By modifying the default Pages widget that comes with WordPress</li>
<li>By applying the filter everywhere wp_list_pages is used</li>
</ol>
Please note that since the second option uses the wp_list_pages hook, the filtering will take place anywhere 
wp_list_pages is used. This includes menu locations to which no custom menu is assigned. Please make sure all your 
menu locations have a custom menu assigned to them to avoid unexpected behavior.
This plugin requires the PHP DOMDocument extension, and PHP5.

RT Filter Page List

Hooks into WordPress core function wp_list_pages, and removes pages from the generated list that are not part of the current navigation path.

adamschoenemann

Usage
Simply install and then find the widget in Appearance->Widgets

Collapsible Pages Widget

Wordpress plugin that provides a widget that lists pages in a collapsible list

RT Filter Page List vs Collapsible Pages Widget