This tree too high

 1. A new 16 x 20 inches with 300dpi canvas is created. i opened my sketch and placed it on the canvas using the Move Tool.

 2. Then, I used the Marquee Tool to select the sketch and I right clicked the sketch and layer via copy

 3 Then, i deleted the previous layer and resized the sketch to fit into canvas

 4 Then I created a new layer (Ctrl + Shift + N)

 5 I start off by painting the first layer. I used oil medium to wet tip brush in wet media category

6 After I am done, I chose a different colour

 7 A new layer is created before I proceed with more painting

 8 Once I am done painting all the green colour, I selected all the layers and grouped the layers together

9 After grouping the layers together, I right clicked the group and selected "group properties" and renamed the group for convenience

 

 10 Then, I created a new layer to paint other parts

 11 This is how it looks like when I am done painting the leaves

 12 Then, I grouped all the layers and renamed the group

 13 Then, I created a new layer again to paint the background

 14 

 15

 16 The layers are grouped accordingly

 17 Layers are grouped accordingly

 18 Ctrl + Shift + Alt + E to merge all the layers into a new layer

 19 Then I clicked "Filter" > "Distort" > "Wave"

 20 Number of generations: 9 ;  Type: Sine ; Wavelength: 10, 300 ; Amplitudes: 5, 10 ; Scale: 100, 100 ; undefined areas: repeat edge pixel

 21 the artwork appear wavy

 22 Then I clicked "Filter", "Artistic", "Poster edges"

 23 Edge thickness: 10, Edge intensity: 4, Posterization: 4

 24 Final Product of This tree too high