Check if the data exist in firebase in c#

Trying to add person information, which contains an ID.

When I insert it everything works fine.

When trying to add another person with the same ID, it got updated.

How can I check if already exists?

person per = new person()
{
    Name = fullNameTbox.Text,
    ID = idTbox.Text
};
var setter = client.Set("Person/"+idTbox.Text,per);