Chebyshev polynomials, Zolotarev polynomials and plane trees

A polynomial with exactly two critical values is called a generalized Chebyshev polynomial. A polynomial with exactly three critical values is called a Zolotarev polynomial. Two Chebyshev polynomials $f$ and $g$ are called Z-homotopic, if there exists a family $p_α$, $α∈ [0,1]$, where $p_0=f$, $p_1=g$ and $p_α$ is a Zolotarev polynomial, if $α∈ (0,1)$. As each Chebyshev polynomial defines a plane tree (and vice versa), Z-homotopy can be defined for plane trees. In this work we prove some necessary geometric conditions for plane trees Z-homotopy, describe Z-homotopy for trees with 5 and 6 edges and study one interesting example in the class of trees with 7 edges.