What are rules to construct binary tree?

To construct a binary tree, follow these rules: each node can have at most two children, referred to as the left and right child; the left child must contain a value less than its parent node, while the right child must contain a value greater than its parent node (for a binary search tree); and each node must be uniquely identifiable, typically using a unique key or value. Additionally, a binary tree can be empty, meaning it contains no nodes at all.