Nonclustered Index Insert
For a single row insert you get a narrow/per-row plan

INSERT INTO SomeTable(SomeString1, SomeString2)
SELECT TOP 1 type, type
FROM master..spt_values




If you select the Clustered Index Insert Operator and View the properties window you can see the same information as shown in the XML.



If you try for 1,000 rows

INSERT INTO SomeTable(SomeString1, SomeString2)
SELECT TOP 1000 type, type
FROM master..spt_values


You get a different wide/per-index plan with the operations split out separately



See Wide vs. Narrow Plans or Craig Freedman's blog for more information about the two