how keep unimported file with rollup?

sorry, i'm not good at english

i want my lib can import subpath,like:pkg/a

but some js file is not import by entryfile,eg:pkg/c. when rollup build, dist does not have these files. this is my config file:

build: {
    target: 'esnext',
    lib: {
      entry: './src/index.ts',
      formats: ['es'],
    },
    minify: false,
    rollupOptions: {
      treeshake: false,
      external: ['big.js', 'dayjs', 'web3', 'ohmyfetch'],
      output: {
        dir: 'dist',
        format: 'es',
        exports: 'named',
        entryFileNames: '[name].mjs',
        preserveModules: true, // Keep directory structure and files
        sourcemap: true,
      },
    },
  },

i try to disabled treeshake, but not work, a solution is export * with all file,but there may be duplicate names，and i don't want to do that either