Top to down traversing of tree is called
Top to down traversing of tree is called Preorder.
Tree traversal is a form of graph traversal and refers to the process of visiting each node in a tree data structure, exactly once. Such traversals are classified by the order in which the nodes are visited.
Unlike linear data structures (Array, Linked List, Queues, Stacks, etc) which have only one logical way to traverse them, trees can be traversed in different ways. Preorder traversal is used to create a copy of the tree. Preorder traversal is also used to get prefix expression on of an expression tree.