addNode(object) {
        // Base insertion index
        let index = this.length;

        // If tree is sorted, insert in correct position
        if (this._tree.config.sort) {
            index = sortedIndexBy(this, object, this._tree.config.sort);
        }

        return this.insertAt(index, object);
    }
Adds a new node. If a sort method is configured,
the node will be added in the appropriate order.

@param {object} object Node
@return {TreeNode} Node object.