@Szymon Stepniak mentions about the map key names being the stage names is incorrect. They're called branch names. They seem relatively unimportant, except for the backend to identify them.

If you run that code it's all nested under the parent stage, "Run"

If you run the below code, you will see they now have individual stages.

def somefunc() {
    stage("Echo1 Stage") {
        echo 'echo1'
    }
}

def somefunc2() {
    stage("Echo2 Stage") {
        echo 'echo2'
    }
}