Entity Framework - Parent Child relational table

Question

I have an Organization entity table

public class Organization
{
    public int OrganizationId { get; set; } 
    public string Name { get; set; }        
    public int OrganizationTypeId { get; set; } 
    public OrganizationType OrganizationType { get; set; }
    public ICollection<OrganizationRelation> OrganizationRelations { get; set; }        
}

then I have my relational table with a self-referencing parent column

public class OrganizationRelation
{
    public int OrganizationRelationId { get; set; }
    public int OrganizationId { get; set; }        
    public int? ParentOrganizationId { get; set; }
    public Organization Organization { get; set; }
    public Organization ParentOrganization { get; set; }
}

public class OrganizationRelationModelConfiguration : IEntityTypeConfiguration<OrganizationRelation>
{
    public void Configure(EntityTypeBuilder<OrganizationRelation> builder)
    {
        builder.HasKey(c => c.OrganizationRelationId);
        builder.Property(c => c.OrganizationRelationId).ValueGeneratedOnAdd();
        builder.Property(c => c.OrganizationId).IsRequired();
        builder.Property(c => c.ParentOrganizationId);            
        builder.HasOne(r => r.Organization).WithMany().HasForeignKey(fk => fk.OrganizationId);
        builder.HasOne(r => r.ParentOrganization).WithMany().HasForeignKey(fk => fk.ParentOrganizationId);
        builder.ToTable("OrganizationRelation", "dbo");
    }
}

When I deploy my db with migration, I see this table created:

CREATE TABLE [mdo].[OrganizationRelation](
[OrganizationRelationId] [int] IDENTITY(1,1) NOT NULL,
[OrganizationId] [int] NOT NULL,
[ParentOrganizationId] [int] NULL,
[OrganizationId1] [int] NULL,
 CONSTRAINT [PK_OrganizationRelation] PRIMARY KEY CLUSTERED
(
[OrganizationRelationId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO

I'm using EF 5.0 I don't get it why is creating the column OrganizationId1