As the TreeDataGrid inherits from DataGrid, the DataGrid does not support items of different type, even if all items in the items-source have a property with the same name. Please provide such support for both controls. 

Please add support for multiple row column headers. As an example of what I'm referring to, see the Telerik UI for Blazor implementation here => Blazor DataGrid Demos - Multi-Column Headers | Telerik UI for Blazor