Here we will see the what is the unrooted binary tree. These trees are connected undirected graph with no cycle. The vertices with one neighbor are the leaves of the tree. Remaining vertices are internal nodes. The degree of the vertices is its number of neighbors. In a tree with more than one node, the leaves are the vertices of degree one.
Free tree is one type of binary tree, where all internal nodes have exactly degree three. In Computer Science, binary trees are often rooted, and ordered, when they are used as data structures, but the applications of unrooted binary trees in hierarchical clustering and evolutionary tree reconstruction are significant.