The latest beta version of WhatsApp with build numbers 2.17.162 or 2.17.163 lets users pin specific chats on top of other chat listings. The number of chats that can be pinned to the top is limited to a maximum number of 3. The latest chats or conversations appear below the pinned chats.
To pin a chat to the top, you will have to long press the chat and you will see the “pin” icon on the top bar. To unpin a chat, long press the pinned chat and tap on the unpin button.
The feature is available on the beta version of WhatsApp. If you want to experience the “pin” feature, you will have to sign up for the beta programme from the Google PlayStore. Or, you can wait for the feature to arrive on the public build version if you don’t want any bugs plaguing you.