/* default state = collapsed (plus shown, dash hidden) */
.tree-view .btn-toggle .icon-expanded { display: none; }
.tree-view .btn-toggle .icon-collapsed { display: inline-block; }

/* expanded state = dash shown, plus hidden */
.tree-view .btn-toggle[aria-expanded="true"] .icon-expanded { display: inline-block; }
.tree-view .btn-toggle[aria-expanded="true"] .icon-collapsed { display: none; }

/* tidy button chrome */
.tree-view .btn-toggle {
  background: none;
  border: 0;
  padding: 0;
  line-height: 1;
}