Might be it will help someone, 4 level and 2 child's on each level
Library.Include(a => a.Library.Select(b => b.Library.Select(c => c.Library)))
.Include(d=>d.Book.)
.Include(g => g.Library.Select(h=>g.Book))
.Include(j => j.Library.Select(k => k.Library.Select(l=>l.Book)))