Basic binary Tree in JavaScript
I can see two obvious points:


Constructor names are usually capitalized, to indicate that they should be invoked with new
You've got some code duplication between bst::insert and node::insert. This even leads to the bug that you don't recognise/handle duplicate values in the root node.


So, I'd suggest:

function Bst() {
    this.root = null;
}
Bst.prototype.insert = function(obj) {
    if (this.root == null) {
        this.root = new Node(obj);
    } else {
        this.root.insert(obj);
    }
};



  I am new to data structures.


Binary trees are a wide field :-) First, I'm missing some other basic operations like searching, traversing, and deleting. If you have mastered these, you can go on with optimizing your tree, e.g. making it a balanced one.