❔ ✅ How to create builder?

I'd like to create builder which should look smth like that:

var schema = new SchemaBuilder()
  .StartGroup("first group")
    .AddText()
  .EndGroup()
  .StartGroup("second group")
    .AddText()
  .EndGroup()

var schema = new SchemaBuilder()
  .StartGroup("first group")
    .AddText()
  .EndGroup()
  .StartGroup("second group")
    .AddText()
  .EndGroup()

I know how to create builder but I don't understand how to create "groups".
All objects inside

.StartGroup()... .EndGroup()

.StartGroup()... .EndGroup()

should have group name
How to do it?