Import Excel (.xlsx) using Power BI API

Hi everybody!
I try to Upload Excel (.xlsx) file to my Power BI using API.  Ability to upload excel files was announced by Microsoft: https://msdn.microsoft.com/en-us/library/mt243840.aspx 
BUT it works just for .PBIX-files, and I can't to realize uploading .xlsx-file
P.S. for importing pbix-file I used multipart./form-data, but it doesn't work for excel.