No, it's Roberts. Article I, Section 3: "The Senate shall have the sole power to try all impeachments. When sitting for that purpose, they shall be on oath or affirmation. When the President of the United States is tried, the Chief Justice shall preside: And no person shall be convicted without the concurrence of two thirds of the members present."
You’re saying that Trump, no longer president, is covered because his alleged offense occurred while he was president. Your reading is not untenable. Yet, the sentence is in the present tense.
In an impeachment of, say, a federal judge, the presiding officer is the President of the Senate (i.e., the Vice President). In practice, this doesn’t happen, and the President pro tempore presides. In the case of a sitting president, there would be a conflict of interest, hence, the Chief Justice. Madison’s notes on the Constitutional Convention are explicit on this substitution. Having said this, the notes aren’t binding. As an aside, it would be inappropriate for the Vice President to preside over his own impeachment, but the Constitution is silent on this.
The Chief Justice, joined if necessary by his colleagues, may have to decide the matter.