I am not much of an artist, But I do have a healthy ability to know when something looks just wrong.
Your duck tree just looks wrong. The tree itself is fine for a cartoony style (Aside from the nonsensical shading at the bottom of the roots.)
However, The other stuff looks like it's just pasted on top of it. If that's an intentional aesthetic then fine, But you should make it known that it's intentional and not just you not making things look right.
Also, The duckbill doesn't look as good as the rest of the tree. The lines are pixelated and the nostril is in the wrong place (The nostrils of ducks are further back, On the raised bit of the bill.)
Overall, It's not terrible, The tree itself is fine for a certain aesthetic, But the additions bring it down.
You could immediately do a bit better just by turning anti aliasing on to reduce some of the pixelation.