Comparison between call money market and Treasury bills market?

Comparison between call money market and Treasury bills market?
The call money market is a market that consists of the borrowing of money by brokers and dealers for the purpose of meeting their credit needs.

Generally, this money is used to either cover their customers' margin accounts or finance their own inventory of securities. Along with day-to-day loans, call money loans play a significant role in interbank money dealing and between banks and money market dealers. The term "call money" alone usually refers to either secured or unsecured callable loans made by banks to money market dealers. Generally, these loans are made on a short term basis.

Treasury bills (also known as T-bills) are the most marketable money market security. Their popularity is mainly due to their simplicity. Essentially, T-bills are a way for the U.S. government to raise money from the public. 

T-bills are short-term securities that mature in one year or less from their issue date. They are issued with 3-month, 6-month, and one-year maturities. T-bills are purchased for a price that is less than their par (face) value; when they mature, the government pays the holder the full par value. Effectively, your interest is the difference between the purchase price of the security and what you get at maturity.

Treasury bills (as well as notes and bonds) are issued through a competitive biddingprocess at auction. If you want to buy a T-bill, you submit a bid that is prepared either non-competitively or competitively. In non-competitive bidding, you'll receive the full amount of the security you want at the return determined at the auction. With competitive bidding, you have to specify the return that you would like to receive. If the return you specify is too high, you might not receive any securities, or just a portion of what you bid for.