EF Using Inheritance for same table, only modify my entity relation, [Discriminator] column show

Question

I have a member class:

[Table("tMember")]
[Bind(Exclude = "TMemberType")]
public partial class tMember
{ }

This class does not have a relationship with the membership class, but I need that relationship. So I would create a new class and inherit from the member class like this:

[Table("tMember")]
public class tMemberInMembership : tMember
{
    public tMemberInMembership()
    {
        trMembership = new HashSet<trMembership>();
    }

    public virtual ICollection<trMembership> trMembership { get; set; }
}

but this class generates a new column, "Discriminator":

  FROM  [dbo].[tMember] AS [Extent1]
INNER JOIN [dbo].[trMembership] AS [Extent2] ON [Extent1].[PersonID] = [Extent2].[PersonID]
WHERE ([Extent1].[Discriminator] = N'tMemberMembership') AND ([Extent2].[StatusMID] = '')

Please Help me..