date-fns: esm tree-shaking not working

The docs show an esm import like this: import { isValid } from 'date-fns';

When bundling this code using webpack, it causes 100% of the date-fns code to be included in the bundle causing the bundle size to increase by approx 82KiB

To reduce the bundle size (tree-shaking), the import must be done like this: import isValid from 'date-fns/isValid';

date-fns: 2.0.0-beta.5 webpack: 4.39.2

See webpack-bundle-analyzer report:

Some useful info on the equivalent issue importing Icons from Material-UI: https://material-ui.com/guides/minimizing-bundle-size/