code: function install(tree, options) {                                        // 37
      if (isObject(tree)) {                                                  // 38
        fileMergeContents(root, tree, options);                              // 39
        if (isFunction(onInstall)) {                                         // 40
          onInstall(rootRequire);                                            // 41
        }                                                                    // 42
      }                                                                      // 43
      return rootRequire;                                                    // 44
    }
docs: 32 33 Merges the given tree of directories and module factory functions     // 34 into the tree of installed modules and returns a require function     // 35 that behaves as if called from a module in the root directory.        // 36