Can't use external Tomcat in MyEclipse

I've added an external Tomcat into Window -> Preferences -> Servers -> Runtime Environments. After that, when I clicking the Run button in the toolbar, MyEclipse keeps running my web app by its embedded Tomcat.

I looked at the Run Configurations but found nothing like "Tomcat Server" except for "MyEclipse Server", which I'm not to use. What's the next step to use external Tomcat?

You've created a new Runtime Environment, but not the Server itself.

1. Bring up the context menu in the Servers view and choose New > Server.
2. In the New Server wizard, in the Server runtime environment combo, select the new runtime environment you defined earlier. Normally you would use the Create runtime environments link here to create the runtime here too, but you can skip this as you've already created one.
3. You will now be able to start your server from the Servers view and from the Run / Debug dialogs.

You can always ask in the MyEclipse forum if you need further assistance, I hope this helps!