focus() {
        if (!this.focused()) {
            // Batch selection changes
            this._tree.batch();
            this._tree.blurDeep();
            this.state('focused', true);

            // Emit this event
            this._tree.emit('node.focused', this);

            // Mark hierarchy dirty and apply
            this.markDirty();
            this._tree.end();
        }

        return this;
    }
Focus a node without changing its selection.

@return {TreeNode} Node object.