If a player disagrees with a judge’s ruling, they may appeal the ruling to the Head Judge.
The ‘right to appeal’ is the right to have your case heard by the most authoritative judge at the event. There is no ‘right to a second opinion’. If the first judge to take your call is the Head Judge, then you just had your case heard by the most authoritative judge at the event. Additionally, judges should not go out of there way to protect the ‘chain of appeals’ because there is no such chain.
In larger, Premier-level tournaments (such as Pro Tour, and Regional Championships), with prior approval, the Head Judge may designate additional Appeals Judges who are also empowered to hear appeals. They will be wearing the same uniform as the Head Judge.
These other judges are called Appeals Judges, and often have the same certifications as the event Head Judge. Additionally, in non-premier level events, the HJ may designate a backup to handle appeals while they are on break, or in the bathroom or in an investigation.
Players may not appeal before the full ruling is made by the responding Floor Judge.
Players are required to be respectful to judges, which includes letting them finish their ruling before disagreeing with them. Players appealing a judge based on perception of the Judge or how they think the judge is going to rule undermines that judge’s authority, and can be considered Unsporting Conduct — Minor.
Rulings made by the Head Judge or designated Appeals Judges are final.
No, you can’t appeal to Wizards or whatever the current Judge Organization is. Yes, it has been tried.