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Lists are not usually considered trees because of their linear structure, whereas a tree can have a branching structure. However, they posses the feature of hierarchy and vertical order that is essential in all kind of trees. A list always has an element followed by exactly one smaller list, meanwhile a tree has an element followed by some number of smaller trees. In this way, a list is a tree in which non-leaf nodes always have exactly one subtree. The lists, are in this way, lianas; long-stemmed woody plants, not constrained in size, they can range from small, indiscrete size, to giant lianas thick as trees that seemingly hang in the middle of the forest. 
% [_data_tree_biology_](http://pipelines.local:9001/p/data_tree_biology)