This tree is not part of eCos itself: it is the directory in which eCos end users write their own applications.
Example applications and their Makefile are located in the component repository, in the directory BASE_DIR/examples.
There is no imposed format on this directory, but there are certain compiler and linker flags that must be used to compile an eCos application. The basic set of flags is shown in the example Makefile, and additional details can be found in Chapter 26.