code: function(xts) {
      return new RoseTree(
        xts.map(function(tree) { return tree.root; }),
        function() {
          return exports.array(xts, tryRemoving);
        }
      );
    }
docs: xtreesToArray :: [RoseTree a] -> RoseTree [a] FIXME: This is duplication of code in types.arrayOf.