ORA-DM-NODES-TREES

*Data Model, Section 4. Nodes*
The second paragraph introduces the notion of "tree". The relationship 
between "trees" and "sequences" (introduced in section 1 "Introduction") 
is not clear.
Specifically, can a tree be a member of a sequence?

Our understanding is: a data set consists of a set of nodes and atomic 
values. The nodes are organized into trees. The most familiar example of 
a tree is an XML document; however, other trees are permitted. Atomic 
values never participate in trees.