To add a chained package, you can do so either by putting the package definition directly under the <Chain> element or by doing a <PackageGroupRef> inside <Chain> to reference a shared package definition.
Here's an example of having the definition directly under <Chain>:
<?xml version="1.0">
<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
<Bundle>
<UX SourceFile="$(ProgramFiles)\src\UI\ux.dll">
<Payload SourceFile="$(ProgramFiles)\src\UI\resources\resources.dll"/>
<PayloadGroupRef Id="ResourceGroupforJapanese"/>
</UX>
<Chain>
<ExePackage
SourceFile="[sources]\packages\shared\MyPackage.exe"
DownloadUrl="http://example.com/?mypackage.exe"
InstallCommand="/q /ACTION=Install"
RepairCommand="/q ACTION=Repair /hideconsole"/>
</Chain>
</Bundle>
</Wix>
Here's an example of referencing a shared package definition:
<?xml version="1.0">
<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
<Bundle>
<UX SourceFile="$(ProgramFiles)\src\UI\ux.dll">
<Payload SourceFile="$(ProgramFiles)\src\UI\resources\resources.dll"/>
<PayloadGroupRef Id="ResourceGroupforJapanese"/>
</UX>
<Chain>
<PackageGroupRef Id="MyPackage" />
</Chain>
</Bundle>
</Wix>