I'd like to go by climbing a birch tree, And climb black branches up a snow-white trunk Toward heaven, till the tree could bear no more, But dipped its top and set me down again.
This appreciation of life doesn't mean he isn't curious. The speaker still wonders about the limits of life and tests out where life ends and heaven begins.
Line 54 has a funny wording that needs to be pointed out: "I'd like to go by…" Usually people talk like this about their own death: "I'd like to go in my sleep." So it seems like the speaker is saying that he'd like to go to heaven by climbing a tree.
However in line 56 he says "Towards heaven," so he doesn't actually want to get to heaven just yet.
In other words, to quote reggae legend Peter Tosh, "Everybody want to go to heaven, / Nobody want to die."
Instead the speaker wants a peek at heaven from the top of the tree, then gently return to his normal life.
That would be good both going and coming back. One could do worse than be a swinger of birches.
The speaker is pleased with this resolution. He likes the idea of a vacation from the troubles of life, as long as it is only vacation and not a permanent situation.
The glimpse at the world from a new perspective would be rejuvenating.
He concludes, like he did in lines 52 and 53, that life's pleasures (like birch swinging) are enough to make life worth living.