Yes, you can invest with a trust. You can add an investor account for your trust here (select "I want to invest with an entity"). If you are the trustee of the trust, you can invest if:
(i) It is a revocable trust and the grantor is accredited; and
(ii) It is an irrevocable trust and either has >$5M assets or all of its beneficiaries are accredited.
You'll also be prompted to upload the Trust Agreement.