If you don’t like the bumps in terrian water then just use a blue smooth plastic brick, You can mess around and try certain tricks like making it slightly transparent then duping the block and moving it downwards to give it a depth type of feel.
If you know the basics of blender then all you really need is a couple squashed down ico sphere for the leaves and screw around with a cylinder for the trunks. If you want branches a neat trick is to add a cube with a sub-surf modifer and mess around with it for some decent roots/branches.
This can be done by messing around with a cube, Pretty basic stuff.
I’d honestly recommend watching a tutorial on the basics of blender, I’d recommend starting off with blender guru’s tutorials as he’s really helpful and explanatory.
These two are a good place to start
I know you already got answers to your other questions in at least a basic form, and I have no idea how to use blender. But, the terrain water in the picture is so flat and smooth because the easiest way to place water is by using part-to-terrain or using the region tool within Terrain tools. If you mess around with the terrain tools you should be able to find the fill tool and then be able to place water.
As for the other questions about the trees and blender;
as I said I am not good with blender. I hope this helped you out!
It depends on what kind of tree your wanting to make a (pine tree, or a tal tree). This could done by using different mesh selections usually a pine tree is created with a cone and cylinder while the trees that have branches or more created, through using a plane and placing a modifier into it (skin). It’ll fill the tree and you could resize the tree to your own liking.
Since your more of a beginner and wanting to learn the blender and the ropes and curves. I would recommend blender gurus beginner tutorial (donut & mug one) is a great place to start, it’s decent in terms of learning the basic tools, techniques, and workflow around blender. He also goes into details and explains everything you could always take notes.
You could even use the blender forum for asking questions and wanting to learn the process or for having issues on different things your stuck on. Here is a thread that has useful information that I would recommend taking along the process:
For the water, ROBLOX has a built in feature for terrain edit that lets you put a water surface. You will find it in “Terrain Editor - Edit - Sea Level” As shown in the picture.
Region is a joke. It has such a small selection box, it’s only useful for moving tiny pieces of terrain around. Not only, you’ll have to move the box with handles, and if you click somewhere else the bounding box will disappear. There are so many problems with regions that I haven’t listed off yet.
Is it a method? Yes. Efficient? No way José.
Part to Terrain is nice, sure, but it is not the most efficient is any way. It will also require tedious copy-pasting, as parts have a maximum size of 2048 x 2048 x2048.
Just use sea level under “Edit.” Want to know how? Read this article:
And scroll down the Sea Level. It’s quick and efficient. Trust me, do not use regions or part to terrain.
Sorry for the late reply, sea level is a niche tool used for its purpose; setting sea levels. The region tool has worked fine for me for a long while, the use of region is to allow developers to move, place, delete, etc large pallets of terrain. The other tools are for as they say, “editing”. I respect your opinion, but the way you go about molding terrain is only as good as your use of the tools. My response is neither wrong nor correct. The, “Haha. No,” is the easiest way to debunk your reply. Just be wary that it is up to the user to decide whether the tools they use are useful to them, not you.
Regions is not a perfect set of tools, but it is still useful.
First off, the OP is not looking to move, place, and delete terrain. They’re looking for sea levels. Does the region tool allow you to move, place, and delete terrain? Yes.
Is that what the OP wants? No.
Secondly, the “large” selection box is still a joke. The maximum size is 512 x 512 x 512, while sea level is 16384 x 16384 x 16384. Tell me that’s the same.
Why should I be wary, or careful? The OP can decide which solution best fits their needs, and I’m not forcing it upon them.
There’s a more efficient way to create a sea. Sea levels.
I feel like you’re not addressing why you believe Region is better than Sea Level, and you’re instead arguing that Region is good for x circumstance.
thanks for reading 
