Hyper-V does not allow to be installed on a machine that's already virtual (such as on another Hyper-V or VMWare). For VMWare, you can circumvent this by adding custom configuration parameters to the VM's configuration.
Add these to the VM's configuration, either through the vSphere (web)client, or by directly editing the VMX-file:
hvh.enable = TRUE
hypervisor.cpuid.v0 = FALSE
If you're editing the VMX-file, you need to enclose the values (behind the =) in double quotes (").
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