Who's the trustee and who's the beneficiary? Capital gain taxes must be paid if they exist so either the trust pays them or the beneficiary pays.
even what is referred to by some as an irrevocable trust is not in some cases.
since you are the grantor, if you are the sole beneficiary the IRS would say this is a grantor trust. such a trust does not pay taxes. the income is actually reported by the grantor/beneficiary on their return.
if it is not a grantor trust, then what are the income distribution requirements? it could be that the gain passes out the the beneficiary who would pay the tax.
if you are not sure about the form and taxation rules, consult the attorney who prepared the trust. if this was a do-it-yourself project, consult a tax advisor.