ement it points to.
        let index = item.dataset.index;
        let el = this.items[index].ref;
        el.click();
      }

      selectTreeElement(item) {
        if (this._previouslySelected) {
          this._previouslySelected.classList.remove('selected');
        }
        this._previouslySelected = item;
        item.classList.add('selected');
      }

      highlight(element) {
        // Find it in the tree.
        let buttons = this.root.querySelectorAll('button');
        if (buttons.length 