function updateShowLines(node) {
    const childrenEl = node.getChildrenElement();
    if (childrenEl) {
      const hideLines =
          !showLines || tree == node.getParent() && !showRootLines;
      /** @suppress {strictMissingProperties} */
      const childClass = hideLines ? node.getConfig().cssChildrenNoLines :
                                     node.getConfig().cssChildren;
      childrenEl.className = childClass;

      const expandIconEl = node.getExpandIconElement();
      if (expandIconEl) {
        expandIconEl.className = node.getExpandIconClass();
      }
    }
    node.forEachChild(updateShowLines);
  }
Recursively walk through all nodes and update the class names of the
expand icon and the children element.
@param {!goog.ui.tree.BaseNode} node