only file name of tree.js or tree.css work

[xd-dw]

i'm using latest nodejs + express + Marko.
i try to integrate this plugin into my project.
After trying many times, i find that only when i change the file names as below, it will work:

jquery.tree-multiselect.js  ---> tree.js
jquery.tree-multiselect.css  ---> tree.css

Even tree1.js does not work...

The structure of my project is as below (working):

i'm backend java developer, having limited knowledge about frontend, maybe someone can help to understand this situation...