There is one way to do that without root.
If you have a device with the Google Play Store, go and download Parallel Space app. If you have an arm/arm64 processor, download its extension Parallel Space 64-bit support as well.
After downloading this app, you can run two accounts of not just Whatsapp, but also of Facebook, Messenger, Instagram, Snapchat etc. This will not affect the first app installed in any way. You don't need to do any switching at all. Just add the shortcut of the Parallel app from Parallel Space on your launcher, and it will launch Whatsapp of the second account.