I'm not a fan of javascript being used for the clicky handlers, even if the element being clicked is a natural clicky element like an anchor tag.

It's much better to rely on a toggle like input type=checkbox and CSS to visualize tree expand and collapse based on checkbox states than to install click handlers in javascript. I suspect you could make such an arrangement more accessible and keyboard navigable as well (via grouping.)

Javascript should only be used to dynamically load/unload subtrees on click in the case of especially huge or costly trees.