Add new child to current node or root.
Remove all children from root and every node in tree.
Distance is the number of edges along the shortest path between two nodes.
Tree is iterated by using `Pre-order Traversal Algorithm"
This function go through tree and counts children. Root element is not counted.
Removes a single instance of the specified node from this tree, if it is present.
A group of nodes with the same parent.
The converse notion of a child, an immediate ancestor.