How can I create a new instance of ImmutableDictionary?

Question

I would like to write something like this:

var d = new ImmutableDictionary { { \"a\", 1 }, { \"b\", 2 } };

(using

Answer 1

Or this

ImmutableDictionary.Empty
   .Add("a", 1)
   .Add("b", 2);

There is also AddRange method available.