How to put Christmas light net on top of very tall tree
9m isn't tremendously tall as trees go. I've worked (a little) with a paint roller extension pole that was about 4.5m long at full extension. If you can rent or buy one or more of these and stand with it on the ladder that'll get you near the top of the tree.
A safer alternative could be scaffolding (rent or buy). Here in the US it is commonly available in units with height about 2m. Two of those would have you standing about 4m above ground; three could have you standing at the same height with safety rails surrounding you to protect against falling. This plus the long paint roller pole could put the top of the tree within your reach -- so long as the tree is relatively columnar in its growth habit and the light netting isn't too heavy to manage on the end of such a long pole/lever.