+6  A: 

How about Root (node with children, but no parent), Node (node with children and parent) and Leaf (node with no children and parent)?

You can then distinguish by name and position within the tree structure (E.g. DepartmentRoot, DepartmentNode, DepartmentLeaf) if need be..

Update Following Comment from OP

Looking at your question, you said that "some" are special, and in your diagram, you have different nodes looking differently at different levels. The nodes may be different in their design, you can build a tree structure many ways. For example, a single abstract class that can have child nodes, if no children, its a leaf, if no parent, its a root but this can change in its lifetime. Or, a fixed class structure in which leafs are a specific class type that cannot have children added to them in any way.

IF your design does not need you to distinguish nodes differently depending on their position (relative to the root) it suggests that you have an abstract class used for them all.

In which case, it raises the question, how is it different?

If it is simply the same as the standard node everywhere else, but with a bit of styling, how about StyledNode? Do you even need it to be seperate (no style == no big deal, it doesn't render).

Since I don't know the mechanics of how the tree is architected, there could possibly be several factors to consider when naming.

Rob Cooper
I don't see a need to distinguish roots from nodes, from leaves.
Zack Peterson
+1  A: 

How about PageTemplate to embody the fact that its children have their own layout, CSS etc?

John Topley
+1  A: 

AreaNode

Daren Thomas
+2  A: 

The word you are looking for is "Section". It's part of a whole and has the same stuff inside.

So, you have Nodes, which have children and a parent, and you have SectionNodes which are the roots of these special subtrees.

Kevin Conner
IMO I think "section" is a little misleading.. I dont think it relates well to actual "tree like" structure..
Rob Cooper
Is it important for the name to reflect the tree structure?
John Topley
+1  A: 

So, it sounds like you are gathering categories. The nodes are the entry points of this categories. How about "TopCategoryNode", "CategoryEntry" then for som,ething that is below them. Or, if you want to divide more, something like "CategoryCSS", "CategoryLayout" etc?

This is kind of generic, but you make clear that there are "categories", and that these do consist of more than one subnode, or subtheme.

Georgi
+1  A: 

Branch ?

Keeps the tree analogy and also hints in this case at departments etc

Thinking about class heirarchies, Root is probably a special case of Branch, which is a special case of Node, special case of Leaf. The Branch/Node distinction is one you get to make for your special situation.

Lot105