Stalin tricked Trotsky to not come to Lenin funeral to damage Trotsky reputation and political. Stalin do most of the things in Lenin funeral like Having a speech. He setting himself up as Lenin disciple.
The Krupskaya gave Lenin secret testament to the central committee. They don't want it to be into the public because it is criticising them and Stalin. Because they wanted Stalin to be the leader but not Trotsky. They thinks that stalin is not a real threat.
The Thirteenth Congress in 1924 saw hostilities out in the open. Zinoviev, Kamenev and Stalin, now effectively a triumvirate leading the party, presented party policy at the congress. Trotsky criticised the party for becoming bureaucratic and less democratic. Despite making brilliant speeches, Trotsky was easily defeated in the votes because the congress was packed with 'well-instructed Stalinist delegates' as well as the powerful blocs controlled by Zinoviev and Kamenev. Trotsky could appealed to supporters inside and outside the party, but he had approved the 'ban on factions' in 1921 and was unwilling to cause splits in the party.
In 1924 Zinoviev have agents Trotsky questioning him his loyalty opposition Lenin before 1917