Hi Stef,

I mean, Tree structure is a standard Data Structure including store, edit and visit. (endorder,preorder).

tree as a struture has a set of protocol for operations. 

TreeStruture is a class of Dolphin ( it has become an opensource project now ).

TreeStructure implements the <treeModel> protocol and organises a collection of objects into a tree like data structure.

You can organise the objects with TreeStructure  when need a tree.  Only one class for all applications. I think.

But in Pharo , there is no such a standard tree structure. so people makes theri owns. 

e.g.

FTDataSource subclass: #FTTreeDataSource

MorphTreeModel subclass: #SpecTreeModel

Model subclass: #MorphTreeModel

Dictionary subclass: #KeyedTree  (not real tree)

these implements mix tree structure and other attributes. 

if we have a standard tree struture, so we can seperate them, make the system become clean and simple.

Best Regards!

Liang