Root
 └─ Node
     ├─ Item
     └─ Item

Node ── Link ── Node

Root — the starting node of a structure.
Node — a structural element that can contain items or connect through links.
Item — a contained element of a node.
Link — a connection between nodes.

        Root
          |
        Node
       /    \
    Item    Item
              |
            Item


Possible alternatives for Item:

Item       — general, simple
Element    — formal, structural
Part       — contained piece
Member     — belongs to a group
Entry      — stored element
Unit       — independent piece
Component  — functional piece
Object     — programming object
Entity     — identifiable thing

Possible alternatives for Link:

Link       — general connection
Edge       — graph theory term
Relation   — abstract connection
Connection — explicit relationship
Path       — directional route

Possible alternatives for Root:

Root       — origin/top
Base       — foundation
Origin     — starting point
Core       — central point

Possible alternatives for Node:

Node       — standard structure element
Element    — generic structure element
Unit       — basic element
Object     — program object
Entity     — identifiable object