Given an array of integers preorder, which represents the preorder traversal of a BST (i.e., binary search tree), construct the tree and return its root. It is guaranteed that there is always possible to find a binary search tree with the given requirements for the given test cases. A binary search tree is a binary tree where for every node, any descendant of Node.left has a value strictly less than Node.val, and any descendant of Node.right has a value strictly greater than Node.val. A preorder traversal of a binary tree displays the value of the node first, then traverses Node.left, then traverses Node.right. Example 1: Input: preorder = [8,5,1,7,10,12] Output: [8,5,10,1,7,null,12] Example 2: Input: preorder = [1,3] Output: [1,null,3] Constraints: 1 <= preorder.length <= 100 1 <= preorder[i] <= 108 All the values of preorder are unique.