Need help with these java question!!!

How do we choose the right data structure for a particular problem?

What is the worst-case, best-case, average-case time complexity of finding a specific key in a BST?

What data structure do we usually use to implement a general tree structure?

What data structure do we usually use to implement a binary heap?

Java coding:

Write a method for in-order traversal of a BST.

Write a method to count the total number of nodes in a BST.

Write a method to perform insertion on a binary heap.