Westpac has priced the top tranche of its latest issue of residential mortgage-backed securities at 85 basis points over the one-month bank bill swap rate - five basis points more than Commonwealth Bank paid on the top tranche of the RMBS deal it did last month.Westpac upsized the issue, Series 2013-2 WST Trust, from the A$750 million offered at the launch to $2.25 billion, a little less than it was thought the bank was seeking to sell.Pricing on the $2.07 billion A tranche, which has a weighted average life of three years, was 85 bps over swap.While Commonwealth Bank's pricing on the top tranche of its $3.2 billion deal was tighter, the weighted average life of the securities was shorter, at 2.5 years.Westpac did not disclose the pricing on the $76.5 million B tranche or on the $103.5 million C tranche.