code: function() {
    if (this.items.length) {
      var f = document.createDocumentFragment();
  
      if (this.config.pagination) {
        var pages = this.pages.slice(0, this.pageIndex);
  
        util.each(pages, function(i, items) {
          util.each(items, function(j, item) {
            appendItem(item, f, this.customOption);
          }, this);
        }, this);
      } else {
        util.each(this.items, function(i, item) {
          appendItem(item, f, this.customOption);
        }, this);
      }
  
      if (f.childElementCount) {
        util.removeClass(this.items[this.navIndex], "active");
        this.navIndex = f.querySelector(".selectr-option").idx;
        util.addClass(this.items[this.navIndex], "active");
      }
  
      this.tree.appendChild(f);
    }
  }
docs: Render the item list
  @return {Void}