% FROM: http://pipelines.local:9001/p/data_tree_biology
% SCION: classification


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. 
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Comparable to botany species, there exist many different kinds of tree graphs, with different branching structures and node contents. For example, in a binary tree the non-leaf nodes always have exactly two subtrees and in a ternary tree they have exactly three subtrees. Each kind of tree has its own class of algorithms to construct trees, traverse trees, and look up information; its own use and own behaviour. 
% [_data_tree_biology_](http://pipelines.local:9001/p/data_tree_biology)

In a context where trees are supposed to have a root, a tree without any designated root is called a free tree. A free tree is an unrooted tree, defined to be a connected graph having no cycles and no size restrictions, the only constraint is to maintain the no loop nature of trees. If any edge of a free tree is deleted, the free tree ceases to exist, as it is no longer connected. In biology, unroot a tree has two possible scenarios: dead or rerooting. there are two ways to reroot plants: in water, and in a rooting medium such as soil. Depending on the plant it requires specific temperature or external chemical components to stimulate root growth.
*Used for example to analyzing networks or showing the structure of hydrocarbons, a graph with no loop & no root.
http://pipelines.local/images/Hydrocarbons_800.gif
% [_data_tree_biology_](http://pipelines.local:9001/p/data_tree_biology)