Complex sentence: What "private label" originators did do was to structure the securities by "slicing" the pooled mortgages into "tranches", each having a different priority in the stream of monthly or quarterly principal and interest stream.
Split into simpler sentences: What "private label" originators did do was to use structured finance. They structured the securities by "slicing" the pooled mortgages into "tranches", each having a different priority in the stream of monthly or quarterly principal and interest stream.