public UploadDefinition( 
   string portalURL,
   Item itemToUpload,
   string[] tags
)

// Create the item to be uploaded, based on a local file
var itemToUpload = ItemFactory.Instance.Create(@"C:\Data\AddToMapCustomItem\AlaskaCitiesXY.csv");
// Define the tags for the item
string[] tags = new string[] { "ArcGIS Pro", "SDK", "Internal Demo" };
// Create the upload definition for the above item
UploadDefinition uploadDefinition = new UploadDefinition(
  ArcGISPortalManager.Current.GetActivePortal().PortalUri.ToString(),
  itemToUpload,
  tags
  );
// Upload the item to the Portal
var result = httpClient.Upload(uploadDefinition);

// Manage the result of the operation appropriately
if (result.Item1 == false)
  return;