Tree (graph theory) - Wikipedia
Wikipedia
Wikipedia's reference article on trees in graph theory, covering equivalent definitions, forests, rooted and ordered trees, spanning trees, and enumeration results such as Cayley's formula. Useful for checking definitions and finding links to related concepts and primary sources.
More resources on Trees
Algorithms, Part I
This course covers the essential information that every serious programmer needs to know about algorithms and data structures, with emphasis on applications and scientific performance analysis of Java implementations. Part I covers elementary data structures, sorting, and searching algorithms. Part II focuses on graph- and string-processing algorithms. All the features of this course are available for free. People who are interested in digging deeper into the content may wish to obtain the textbook Algorithms, Fourth Edition (upon which the course is based) or visit the website algs4.cs.princeton.edu for a wealth of additional material. This course does not offer a certificate upon completion.
Wolfram MathWorld
MathWorld is an online mathematics encyclopedia from Wolfram Research offering detailed, browsable articles on topics across the math spectrum, including algebra, geometry, calculus, and number theory. Each entry includes definitions, theorems, formulas, diagrams, worked examples, and links to further reading.
Art of Problem Solving - Trees
A short Art of Problem Solving wiki entry on trees in graph theory, stating the definition of a tree as a connected acyclic graph, the n-1 edge property, forests and rooted trees, aimed at students preparing for math competitions.
Graph Theory
Learn graph theory focusing on trees with Dr. Sarada Herke! Explore fundamentals and applications in this comprehensive course.
Diestel Graph Theory
Official site for Reinhard Diestel's Springer graduate text, where the main text is readable free online and paid eBook editions add the full apparatus. It covers matching, connectivity, planarity, colouring, flows, extremal theory, and minors.
Mathematics for Computer Science (MIT 6.042J)
Discrete mathematics for computer science with an emphasis on definitions and proofs: logic, induction, sets and relations, graph theory, modular arithmetic, asymptotics, counting and discrete probability. 25 lecture videos, problem sets and exams with solutions build fluency in writing proofs.