If a president is impeached the trail will be presided over by?

The Chief Justice. The impeachment process is discussed in Article 1, Section 3, Clause 6: "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."