3. Tree branches
With the Pen Tool, create some wavily stroke paths and fill stroke color with green. Then apply these paths with the Art Brush you've created in the previous step. Adjust the Opacity between 40-50% so it blends with the tree. If you want bigger tree branches, apply thicker stroke weight, thinner stroke = smaller branches. Play around with the Opacity and Stroke Weight and try to make the tree looks as natural as possible.
4. Christmas balls
Create various size and gradient Christmas balls with the Ellipse Tool. Place some on top of the tree, send some to the back, and put some behind the branches.
5. Light bulbs
The tree still looks too plain, we need some more decorative lights. Create some light bulbs as shown on the left, drag it to the Brushes Library to make a New Scatter Brush.
Scatter Brush Options
When the Scatter Brush Options window popup, select Random for all options and enter the range values as shown below.
More Vector Graphics: 
