Convert BST to Greater Tree


 can someone please explain how does 2 > 5 > 13 become 20 > 18 > 13
 How is this a Greater Tree? what does Greater tree even mean ?
 it directly jumps to saying reverse inorder traversal... looking online, reverse inorder traversal is we first traverse all noes (left and right) before traversing its parent... so i am confused :(

here is what others say about reverse in order traversal
http://algorithms.tutorialhorizon.com/reverselevelordertraversal/

@seakhar The link you posted is about a reverse levelorder traversal.
 Each node has the values of all greater nodes added to its value. Said another way, each node has the sum of values in its right subtree added to its value.
 I don't think "Greater Tree" is a real thing elsewhere.
 A reverse inorder traversal traverses the nodes in descending value. At least, it does in a BST. An inorder traversal is not welldefined for arbitrary trees.