Any orthogonal polynomial family can be combined into a simple tensor product basis. So in your case you could try T_1(x), T_1(y), T_1(x)T_1(y), T_2(x), T_2(x)T

Any orthogonal polynomial family can be combined into a simple tensor product basis. So in your case you could try T_1(x), T_1(y), T_1(x)T_1(y), T_2(x), T_2(x)T_1(y), and so on.