The routines here are responsible for reading the .trl file and storing the data in the headTreeList variable. Effectively headTreeList acts solely as the data structure containing the raw data read from the file. The application later builds other data structures from headTreeList that are actually used as the application's data abstractions. One might consider headTreeList as a file interface and nothing more.
The data read from the .trl file is stored in headTreeList. The access routine findTreeList finds the record corresponding to the stand identifier passed as a parameter.