create AssetBundleBuild with more files

hi all! I wish create an assetbundle that contains some text files that are textassets into my project..
the strange thing is if I do this:

Code (CSharp):

1. AssetBundleBuild buildInfo = new AssetBundleBuild { assetBundleName = "textAssets.unity3d",
2.     assetNames = new [] {"Assets/firstFile.txt"}};
3. }

it works and create an textAssets.unity3d with the file inside, but if I do this:

Code (CSharp):

1. AssetBundleBuild buildInfo = new AssetBundleBuild { assetBundleName = "textAssets.unity3d",
2.     assetNames = new [] {"Assets/firstFile.txt", "Assets/secondFile.txt"}};
3. }

it doesn't work, seems that I need to create a assetbundle for each prefab/file.txt
thanks for your help