remm

This plugin provide widget that display a list with categories and posts in your sidebar. 
Widget can save the opened categories, and use cache.

Wp Ajax Tree

This plugin provide a widget that display a category and pages tree on your sidebar, using ajax to collapse categories.

cjyabraham

👩‍👩‍👧‍👧 📄 🌲 Adds a “Clone Page Tree” action to the page/post row actions. Cloning a page tree clones the page and all descendents creating a new copy of the full hierarchy. After clicking “Clone Page Tree” you will be redirected to edit the top-most page to allow you to give it a unique title. All cloned pages are left in draft mode.
There are <a href="https://wordpress.org/plugins/search/duplicate/" rel="ugc">many plugins out there</a> which allow you to duplicate a post or page however this is the only one that allows you to duplicate a page and all its descendent pages in a single click.
Code is stored in this <a href="https://github.com/cncf/clone-page-tree" rel="nofollow ugc">github repo</a>.
The plugin has been developed for <a href="https://www.cncf.io/" rel="nofollow ugc">CNCF</a> and <a href="https://www.linuxfoundation.org/" rel="nofollow ugc">The Linux Foundation</a>.

Clone Page Tree

👩‍👩‍👧‍👧 📄 🌲 Adds a "Clone Page Tree" action to the page row actions to duplicate an entire page hierarchy.  Also works for CPTs and posts.

Wp Ajax Tree vs Clone Page Tree