National Australia Bank's Bank of New Zealand has finally entered the fast-growing KiwiSaver retail funds management business almost six years after it started. It has registered its own scheme with the Financial Markets Authority. BNZ previously offered its customers an AXA scheme, while the other three big Australian-owned banks, ANZ, Westpac and CBA's ASB, offered their own schemes.Both ANZ and ASB were picked as default providers to the government-subsidised scheme when it began in 2008.  Westpac has been aggressively building its KiwiSaver scheme too.  These three big banks have NZ$5 billion in funds under management in KiwiSaver schemes, making up 35 per cent of the NZ$14 billion under management in all KiwiSaver schemes.  ASB, which manages its own funds, is the market leader, with NZ$2.6 billion, while Westpac, with NZ$1.7 billion, and ANZ, with NZ$656 million, are next in line.  Westpac's funds are managed by BT Funds Management and ANZ's are managed by its wholly owned OnePath. ASB has been particularly effective at investing its KiwiSaver Conservative fund in its own term deposits, helping it to meet its mandated liquidity and core funding requirements. ANZ has struggled to replicate its overall market dominance, given the struggles of OnePath's predecessor ING, whose big losses in funds were linked to its collateralised debt obligations when KiwiSaver was launched in 2008.Westpac has been relatively successful in building up its number two position despite not being a default provider. KiwiSaver customers are offered a NZ$1,000 kickstart from the government and receive an annual government contribution, but are able to opt out of the scheme. Funds are deducted by the Inland Revenue Department when a new employee starts a job and then automatically placed in one of six default schemes. The saver can then opt out of the scheme or switch to another fund. The average saver contributes about five per cent of his or her income, significantly less than the nine per cent contributed in Australia.BNZ is getting into the market just as it is maturing. Just over two million New Zealanders, or about 50 per cent of those eligible, have accounts, although about 250,000 have since opted out or suspended contributions. Most believe the scheme is near saturation point, although there is a concerted campaign by the savings industry to turn the voluntary scheme into an Australian-style compulsory one, which would make it much more attractive for banks with their own funds management schemes.