Is there a Linq method to add a single item to an IEnumerable?

Question

Basically I am trying to do something like this:

image.Layers

which returns an IEnumerable for all layers except the Parent layer,

Answer 1

Append and Prepend have now been added to the .NET Standard framework, so you no longer need to write your own. Simply do this:

image.Layers.Append(image.ParentLayer)

See What are the 43 APIs that are in .Net Standard 2.0 but not in .Net Framework 4.6.1? for a great list of new functionality.