Bundling MSIX packages
Overview
An MSIX bundle is made up of multiple MSIX packages and it can reduce the size of the app that users download. App bundles are helpful for different architectures, language-specific assets, varying image-scale assets, or resources that apply to specific devices. By bundling multiple architectures versions of your application into one entity, only the bundle needs to be uploaded to your distribution location (instead of having one for each architecture). The Windows 10 deployment platform is aware of the .msixbundle package type and will only download the files that are applicable to a device's architecture. Keep in mind that if you decide to distribute an .msixbundle for a particular app, you cannot revert back to distributing just an MSIX package.
If you're packaging your application in Visual Studio, the Create Package Wizard gives you a "Generate app bundle" option during package creation. You can set this option to have Visual Studio generate an MSIX bundle for you. If you're generating MSIX packages using the MSIX Packaging Tool or MakeAppx.exe you can take advantage of MakeAppx.exe to generate a bundle from individual packages e.g. after generating or converting an x86 and x64 MSIX package of your app you can use the process outlined below to bundle the packages using MakeAppx.exe.
Additional Resources
For more information about generating an MSIX bundle see:
For more information about signing app packages with SignTool.exe, see this article.