Does Webpack tree shaking with dead code elimination work on node_modules?

Considering this Webpack 3.8.1 config.

// common
module.exports = {
        context: path.resolve(__dirname, './src'),
        entry: [
            'whatwg-fetch',
            './index'
        ],
        output: {
            path: path.resolve(__dirname, 'build/assets'),
            publicPath: '/assets/',
            filename: 'main.js'
        },
        plugins: [
            new CleanWebpackPlugin(['build']),
        ],
        module: {
            rules: [{
                test: /\.js$/,
                exclude: /node_modules/,
                use: {
                    loader: 'babel-loader',
                }
            }, {
                test: /\.(scss|css)$/,
                use: [{
                    loader: 'style-loader'
                }, {
                    loader: 'css-loader'
                }, {
                    loader: 'sass-loader'
                }],
            }, {
                test: /\.(png|jpg|gif|woff2|woff)$/,
                use: [
                    {
                        loader: 'url-loader',
                        options: {
                            limit: 8192
                        }
                    }
                ]
            }]
        }
    };

//prod
module.exports = merge(common, {
    plugins: [
        new webpack.DefinePlugin({
            'process.env.NODE_ENV': JSON.stringify('production')
        }),
        new UglifyJSPlugin()
    ],
    devtool: 'none'
});

and this Babel 6.26.0 config

{
  "presets": [
    [
      "env",
      {
        "modules": false,
        "targets": {
          "browsers": [
            ">1%"
          ]
        }
      }
    ], [
      "react"
    ]
  ],
  "plugins": [
    "transform-class-properties",
    "transform-export-extensions",
    "transform-object-rest-spread",
    "react-hot-loader/babel"
  ]
}

I was expecting that tree shaking alongside with dead code elimination of UglifyJS should work in a way that enables me to write named imports from index.es.js modules, for example Material-UI-Icons and unused ones get removed from the bundle.

import {Menu} from 'material-ui-icons';

This library does indeed reexport ES6 modules defined in package.json as "module": "index.es.js".

Yet my bundle size increased by 0.5MB after importing single icon. When I changed it to

import Menu from 'material-ui-icons/Menu;

bundle size got reduced again with only this icon imported.

Is there something wrong in my configuration, or do I missunderstand how tree shaking works and does not apply to this scenario?