Collection Tree : Public view more design

All of the HTML is generated by PHP--there are no static HTML pages. If what you're displaying there is intended to be the public view of Collection Tree, it would (I think) be in yourtheme/collection-tree/index/index.php

You might want to take a look at one of the themes put out by CHNM (Thanks Roy, Berlin, Seasons) to get an idea of how themes are structured:
http://omeka.org/add-ons/themes/

You can read more about the technical details of themes (assuming you're using 2.x) at

http://omeka.readthedocs.org/en/latest/Tutorials/index.html#modifying-themes

By creating that file in your theme (or any of the php files in plugins/CollectionTree/views/shared), the default view (which generates the HTML) of the plugin will be overwritten by the view used in your theme. You can overwrite the file in the plugin folder, but then you would lose your customizations every time the plugin is upgraded.