a leaning tree

Question

This is an Australian pine at least 5-6 yrs old and is over 20 ft tall and trunk is approx 5 inches in diameter. It grew straight but is now leaning.

Answer 1

Austrian Pine trees are quite disease resistant but they can become infected with a root feeding nematode.
Phytophthora and Hetrobasidion root rots.
Have you had excessive rain to loosen the ground and root system?
With the size of tree your dealing with I would certainly have a professional arborist look at the tree to determine the best coarse of action.

Here are a couple of links for you.
https://www.gardeningknowhow.com/ornamental/trees/tgen/straighten-tree.htm
https://extension.psu.edu/pests/plant-diseases/all-fact-sheets/pine-diseases