Saving specific data type to a collection

I want to save data to a rich content field in a collection from backend code.

Currently, it saves, but as plain text (i think) and I need to manually go into the collection via the Portal to convert the type to Rich Content within the collection.

Im currently using the bulkInsert method.

Is there a way to set the type of the data when inserting into a collection, or is there a way to update the content to Rich Content after its been inserted i.e. by writing a job that runs and converts the data