Onetomany entering a new record?

Question

I am trying to create a Onetomany relationship between 2 classes "User and Broker" where 1 User has many Brokers. The problem is when I add a new Broker a new User is created and I don’t know why it happens

How to solve this?

User

public class Usuario
{         
    public long id { get; set; }

    public String nome { get; set; }    

    public IList<Corretora> corretoras { get; set; }
}

Broker

public class Corretora
{        
    public long id { get; set; }

    public String nome { get; set; }    

    public Usuario usuario { get; set; }
}

User

public class UsuarioMap : EntityTypeConfiguration<Usuario>
{
    public UsuarioMap()
    {
        this.ToTable("Usuarios");
        this.HasKey<long>(u => u.id);
        this.Property(u => u.id)
            .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);

        this.Property(u => u.nome).IsRequired().HasMaxLength(50);

        //um usuario tem muitas corretoras
        HasMany(u => u.corretoras).WithRequired(c => c.usuario);
     }
 }

Brokeramap

public class CorretoraMap : EntityTypeConfiguration<Corretora>
{    
    public CorretoraMap()
    {
        this.ToTable("Corretoras");
        this.HasKey<long>(c => c.id);
        this.Property(c => c.id)
            .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);

        this.Property(c => c.nome).IsRequired().HasMaxLength(50);       

        HasRequired(u => u.usuario).WithMany(c => c.corretoras);
     }
 }