Mr Cunliffe also said he did not know who the two donors who had refused to be publicly named were.
Prime Minister John Key said that was not credible and he should name the two donors. "Clearly there is something going on about people who gave money but know if their identity is in the public domain, that would be very untidy for the Labour Party."
Mr Cunliffe apologised to his caucus for a "lapse in judgment" by using the trust. Labour MP Shane Jones has listed his donors in the register for Pecuniary Interests, but that will not be released publicly for up to three months.
Mr Cunliffe initially refused to confirm a trust was used for his campaign when the Herald asked about it early this week. It allows him to avoid disclosing individual donations in the Register for Pecuniary Interests. After admitting to using a trust a day later, he said it was "common practice" in politics and was not illegal. Yesterday he said he had asked the trustee to check whether the donors would be named and to return donations to any who would not. Asked if he would have taken the step of voluntary disclosure today had it not been for media pressure, he said he had been reflecting on it over the last week.
"I don't think in hindsight that a trust structure fully represented the values I would like to bring to this leadership. Decisions that were made to set up the trust could have been better. I have learned from that and am now making sure I do whatever I can to ensure transparency."
The TR Trust will be listed in Mr Cunliffe's return to the Register of Pecuniary Interests under the "discharged debts" section, which requires disclosure of debts the MPs owe which are paid by a trust.
Mr Presland said he did not wish to comment.
Trust donations
Donations of more than $500 to the TR Trust for David Cunliffe's leadership bid.
Known: Total of $9500 from
* Selwyn Pellett: businessman, regular donor to Labour and Mr Cunliffe. Openly backed Mr Cunliffe in the leadership race.
* Tony Gibbs: businessman, former right-hand man to Sir Ron Brierley. Has previously donated to Act and National as well as Labour.
* Perry Keenan: senior partner at Mr Cunliffe's old employer, the Boston Consulting Group in Chicago. Old friend and work colleague.
Unknown: Total of $8300 from
* Two unknown donors, either individuals or companies. Money will be returned because they refused to be named.