HomeController.cs

//Demo usage

public class HomeController : MyControllerBase
{
    private readonly IRepository<MyEntity> _myEntityRepository;

    public HomeController(IRepository<MyEntity> myEntityRepository)
    {
        _myEntityRepository = myEntityRepository;
    }

    public ActionResult Index()
    {
        var entities = new List<MyEntity>
        {
            new MyEntity(),
            new MyEntity(),
            new MyEntity()
        };

        _myEntityRepository.Insert(entities); //using the new extension method

        return View();
    }
}

MyRepositoryExtensions.cs

using System;
using System.Collections.Generic;
using System.Reflection;
using Abp.Domain.Entities;
using Abp.Domain.Repositories;

namespace MyProject
{
    //Add this class to .Core project

    public static class MyRepositoryExtensions
    {
        public static void Insert<TEntity, TPrimaryKey>(this IRepository<TEntity, TPrimaryKey> repository,
            IEnumerable<TEntity> entities)
            where TEntity : class, IEntity<TPrimaryKey>, new()
        {
            var type = Type.GetType("MyProject.MyRepositoryHelper, MyProject.EntityFramework");

            var bulkInsertMethod = type.GetMethod("BulkInsert", BindingFlags.Static | BindingFlags.Public);

            var genericMethod = bulkInsertMethod.MakeGenericMethod(typeof(TEntity), typeof(TPrimaryKey));

            genericMethod.Invoke(null, new object[] { repository, entities });
        }
    }
}

MyRepositoryHelper.cs

using System.Collections.Generic;
using Abp.Domain.Entities;
using Abp.Domain.Repositories;
using Abp.EntityFramework.Repositories;

namespace MyProject
{
    //Add this class to .EntityFramework project

    public static class MyRepositoryHelper
    {
        public static void BulkInsert<TEntity, TPrimaryKey>(IRepository<TEntity, TPrimaryKey> repository, IEnumerable<TEntity> entities)
            where TEntity : class, IEntity<TPrimaryKey>, new()
        {
            var dbContext = repository.GetDbContext();
            dbContext.Set<TEntity>().AddRange(entities);
        }
    }
}

Demonstrates how to extend standard IRepository interface. Adds a Insert overload that gets a list of entities.