First, you have to learn how to climb a tree with a camera on a tripod strapped to your back.
Next, you need to learn how to use that camera while standing on a ladder on the branches of the tree. A few years of experience as an acrobat or a tight rope walker at a local circus may help here.
These pictures are from a book called Wild Life At Home by R. Kearton published in 1901. I found it on Google Books.
Kearton explains their technique for those folks who are dying to try it out in their backyard:
...my brother puts on a pair of climbing-irons, and ascends with his camera slung upon his back...In many cases the legs of the tripod may be lashed to convenient branches close to the nest to be photographed, but in some this is impossible on account of their extreme slenderness. In cases of this kind we hoist a ladder up and lash it in a position as nearly perpendicular as possible, in order to reduce the leverage produced by the photographer's weight to a minimum, and, ascending above it, fix the camera...
The Kearton Brothers' problem was that their camera was too bulky and heavy to be hand-held; they always needed a tripod.
They seem to have been talented naturalists and photographers. Unfortunately, the print quality of their book doesn't do justice to their pictures.