webpack: Treeshaking doesn't take place - lodash

Do you want to request a feature or report a bug? Bug?

What is the current behavior? I am loading a single export from lodash, but get the complete lodash in output-bundle.js.

If the current behavior is a bug, please provide the steps to reproduce.

page1.ts

import {add} from "lodash"
alert(add(5, 5));

Webpack.config.ts

// import { Options, Configuration, optimize, RulesRule } from "webpack";
import * as webpack from "webpack";
const path = require('path');
const UglifyJSPlugin = require('uglifyjs-webpack-plugin');
const cleanPlugin = require("clean-webpack-plugin");

let config: webpack.Configuration = {
  mode: "production",
  devtool: false,
  entry: {
    page1: "./src/pages/page1",
    page2: "./src/pages/page2"
  },
  optimization: {
    sideEffects: false
  },
  output: {
    filename: '[name].js',
    chunkFilename: '[name].js',
    path: path.resolve(__dirname, 'dist')
  },
  resolve: {
    extensions: [".ts", ".js", ".txt", ".json", ".css", ".less", ".scss", ".saas"],
    alias: {
      "#comp": path.resolve("./src/components/")
    }
  },
  module: {
    rules: [
      {
        test: /\.ts$/,
        loader: "ts-loader"
      },
      {
        test: /\.(less|css)$/,
        use: [{
          loader: 'css-loader',
          options: {
            sourceMap: true
          }
        }, {
          loader: 'less-loader',
          options: {
            sourceMap: true
          }
        }]
      }]
  },

  plugins: [new cleanPlugin("dist"),
  new UglifyJSPlugin({
    uglifyOptions: {
      warnings: true,
      mangle: false,
      output: {
        beautify: true,
        comments: true
      }
    }
  })
  ]
}

module.exports = config;

What is the expected behavior? Treeshaked output. If this is a feature request, what is motivation or use case for changing the behavior?

Please mention other relevant information such as the browser version, Node.js version, webpack version, and Operating System. Win10 x64 webpack 4.4.1 node 8.10