Adding Trees to Java: Data Structures

[edengarza]

Adding a section for trees. It includes:

• a description of what trees are at a high level,
• a simple description of binary trees,
• an overview of how to traverse a tree,
• an activity where they more or less program binary search

Remaining Item before merging:

• Add pictures visualizing trees and traversing them

[ozhang22]

Small comments for now