nested user control in wpf without view and model

i have an application in wpf which is not based on mvvm. in this i am to use a usercontrol for chat message which is used in another usercontrol chatmessagelist and chatmessagelist use in mainwindow.xaml.  i am not using mvvm and all code on code behind. how to use obsavablecollection for chatmessages in list. please help me out.

 

 

thanks

nirmal