What is the design for a dynamic tree list?

Question

Design

I am designing a website in flat style.
There is a dynamic list in the form of a tree:
Section 1
Section 1.1.
Section 2
....
I want to create a beautiful and simple design, but I don't know what to apply or in what form to do it. Do not tell me?

Answer 1

It all depends on the purpose of such a tree-like list.
If each Section of the first level should be constantly in sight - this is one thing. If the user will need to "dive" deep into the hierarchy and perform actions there - another thing.
Most likely ux.stackexchange (tag: tree) has the answer. The principles of displaying such a list are the same, and flat design is just the tip of the iceberg, graphic design.
For inspiration:
Kendo UI example
Vertical navigation in modern admin panels
Another example
Using collapse-expand panels - left sidebar with navigation (also a kind of tree, where there is a Section and a Subsection)