This is the 12738th most frequent German word.
wipfeln
"To form or be at the treetops."
Here, 'wipfeln' is used to describe the gradual rocking motion of treetops in response to wind.
Die Zwergkronenfichten im Park wipfeln sanft im Wind.
The dwarf crown firs in the park sway gently in the wind.
Used as a noun derivative 'wipfeln' here, it signifies the visible motion of treetops.
Nach dem Sturm konnte man noch das Wipfeln der Bäume beobachten.
After the storm, one could still observe the swaying of the trees.
In this artistic context, the motion implied by 'wipfeln' is imbued with symbolic meaning.