How to run several tasks as a group?

I created two tasks to assist me in the development of a web site:

{
    "version": "2.0.0",
    "tasks": [
        {
            "taskName": "build site",
            "command": "jekyll b --watch --incremental",
            "type": "shell",
            "group": "build"
        },
        {
            "taskName": "serve site",
            "command": "./_devd -ol _site",
            "type": "shell",
            "group": "build"
        }
    ]
}

I can start them one by one with F1 → Run Task (so I need to issue the sequence twice, once for each task) and I end up with two tasks running at the same time.

Is it possible to automate this and run a group of tasks at the same time? I thought that the group entry would, well, group them together but it is not the case (they are just recognized as belonging to the build or test group - and I did not find a way to start the whole group at once).