If you want to do it yourself with a bow-saw, perhaps the safest way is:
1 tie a rope to the branch
2 climb tree and cut branch – but not completely (you’ll learn to judge how much…)
3 climb down off tree, pull rope to break branch
(3b climb back up to complete the cut if necessary)
repeat for all branches…
If you want to use a chainsaw, it’s easier:
1 phone up a tree surgeon
2 sit back and watch
30ft is not all that huge, if you’ve got patience and common sense it should be ok. But still, not with a chainsaw unless you’ve got space to fell it in one (ie, there’s nothing that matters within range of the tree).