Chaining on where clause using OR operator #linq

LINQChainingOrWhereClauses.cs

        public IEnumerable<MyEntity> GetMyEntitys(IEnumerable<long> MyEntityIds)
        {
            IEnumerable<IEnumerable<long>> segmentedMyEntitys = MyEntityIds.ToArray().Split(100);

            IQueryable<EF.MyEntity> x = from MyEntity in _dbContext.MyEntitys select MyEntity;
                       
            Expression<Func<EF.MyEntity,bool>> expression = null;
            foreach (IEnumerable<long> segmentedMyEntityIds in segmentedMyEntitys)
            {
                Expression<Func<EF.MyEntity,bool>> y = p => segmentedMyEntityIds.Contains(p.MyEntityId);              
                if (expression == null) {
                    expression = y;                    
                }    
                else 
                    expression =  expression.Or(y);
            }
                        
            IQueryable<EF.MyEntity> z = x.Where( expression );
            return z.Select(_MyEntityRowConverter.Convert);
        }
        
            public static class PredicateBuilder {

        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> a, Expression<Func<T, bool>> b) {    

            ParameterExpression p = a.Parameters[0];

            SubstExpressionVisitor visitor = new SubstExpressionVisitor();
            visitor.subst[b.Parameters[0]] = p;

            Expression body = Expression.AndAlso(a.Body, visitor.Visit(b.Body));
            return Expression.Lambda<Func<T, bool>>(body, p);
        }

        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> a, Expression<Func<T, bool>> b) {    

            ParameterExpression p = a.Parameters[0];

            SubstExpressionVisitor visitor = new SubstExpressionVisitor();
            visitor.subst[b.Parameters[0]] = p;

            Expression body = Expression.OrElse(a.Body, visitor.Visit(b.Body));
            return Expression.Lambda<Func<T, bool>>(body, p);
        }   
    }

    internal class SubstExpressionVisitor : ExpressionVisitor {
        public Dictionary<Expression, Expression> subst = new Dictionary<Expression, Expression>();

        protected override Expression VisitParameter(ParameterExpression node) {
            Expression newValue;
            if (subst.TryGetValue(node, out newValue)) {
                return newValue;
            }
            return node;
        }
    }