Saddle sizes

Quick question. Looking at used saddles. One saddle says “medium tree”. Next saddle described ’ 4" tree.’ What the dickens are they talking about, a 4" tree?? Where does the 4" com in, and how does that inform the size of the tree?

If there are tree sizes in inches, can they be related to narrow, med-wide, wide, etc?

Really really grrrr.

Brands of saddles will all vary slightly. a 4" tree is usually just the measurement front felt dot to felt dot across the front of the saddle. 4" would usually be a medium I think, if not bordering on slightly narrow for a medium.

Saddle measurements between many brands are so inconsistent. UK saddles are measured in degrees of angles such as 85 degrees. When someone lists a width in inches, it needs to be qualified as to where but it is hard to compare to others if they are not measured in the same way and same distance from the peak, etc.