The B.O.M. can be considered as containing all levels of the product and the Product tree can also be considered as doing the same.
So what is the advantage of having two terminologies and what actually seperates them?
or are they the same thing?

 

In a simple product where all of the components go into a single assembly, there is really no difference between the two.

When you have a complex assembly, particularly if an individual subassembly is used multiple times in the end item, the tree helps narrow down just the items required to build the subassembly unit. Trying to wade through a BOM list to gather parts kits would be extremely difficult.

In a simple BOM list for a one-level assembly, it's easy to keep track of what's required to build the end item. However, with a complex assembly that has multiple levels of sub-assemblies, the BOM list becomes somewhat complex. Each component needs to have a link to what assembly or assemblies it is used on, the quantity required, and the find numbers (reference designators) on the drawings/schematics.

There are many more ways to look at complex assemblies than a BOM or drawing tree. Each way of arranging the data has it's own uses.

Many years ago, I used an IBM mainframe and a Calcomp high-speed plotter to plot a moderately detailed drawing tree of the radar assemblies for the F-14D Tomcat program.
It was 36" tall and 40 feet long.