Locally served SPFx webpart not loading in the workbench.

I have created a new webpart for a sharepoint site using SPFx. But after using `gulp serve` the webpart is not loading in the workbench. It shows the following warning:

Warning

Your web part will not appear in the toolbox. Please make sure "gulp serve" is running in a web part project. Please refresh the page once "gulp serve" is running.

Note: I have installed the certificate using `gulp trust-dev-cert` But still I am getting the same error.