The phrase "great oaks" refers to mature and strong oak trees. It is often used metaphorically to represent someone or something that is powerful, influential, or of great importance. Full definition
Like they say about great oak trees, it starts from a little acorn and that's the acorn you are seeing right now,» says Leslie Oghomienor, Barcelona's partner and the school's administrator. (nigeriapoliticsonline.com)
But from such acorns grow great oaks of bad money advice. (badmoneyadvice.com)
From tiny acorns do great oaks grow; that analogy fits perfectly with N + +. (gamestm.co.uk)